Photocurable ink composition for ink jet recording and ink jet recording method

ABSTRACT

The present invention provides a photocurable ink composition for ink jet recording with excellent curability. The photocurable ink composition for ink jet recording includes polymerizable compounds, a photopolymerization initiator, and a colorant, wherein the polymerizable compounds include a vinyl ether group-containing (meth)acrylate represented by general formula (I): 
       CH 2 ═CR 1 —COOR 2 —O—CH═CH—R 3   (I)
 
     (wherein R 1  is a hydrogen atom or a methyl group, R 2  is a divalent organic residue having 2 to 20 carbon atoms, and R 3  is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms) and phenoxyethyl (meth)acrylate.

BACKGROUND 1. Technical Field

The present invention relates to a photocurable ink composition for inkjet recording and an ink jet recording method using the same.

2. Related Art

Various methods have been used as recording methods for forming imageson recording media such as paper on the basis of image data signals.Among these methods, an ink jet method uses a low-cost apparatus andforms images directly on recording media by ejecting inks only tonecessary image portions, and thus the ink jet method can efficientlyuse inks and requires a low running cost. Further, the ink jet method isexcellent as a recording method because of its low noise.

In the ink jet recording method, photocurable ink compositions which arecured by light irradiation have recently been used as ink compositionscapable of imparting good water resistance, solvent resistance, andabrasion resistance.

For example, Japanese Patent Nos. 3461501 and 3544658 disclose an inkcomposition containing 2-(vinyloxyethoxy)ethyl (meth)acrylate, at leastone of 2-(hydroxyethoxy)ethyl vinyl ether and diethylene glycol divinylether, diethylene glycol di(meth)acrylate, and a photopolymerizationinitiator, and a reactive diluent composition ([0114] and Table 1 in[0139] of Japanese Patent No. 3961501, and Examples and Tables 1 and 4of Japanese Patent No. 3594658).

For example, Japanese Unexamined Patent Application Publication No.2009-62591 discloses an ink jet ink containing 69.82 parts by weight ofpropoxylated neopentyl glycol diacrylate, 10.0 parts by weight ofbifunctional vinyl ether monomer (a compound having only a vinyl ethergroup as a substituent), a radical photoinitiator, and 3.60 parts byweight of a disperse pigment, and having a viscosity at 25° C. of 22mPas ([0021] and [0022] of Japanese Unexamined Patent ApplicationPublication No. 2009-62591).

For example, Japanese Unexamined Patent Application Publication No.2008-179136 discloses an ink solution containing2-(2-vinyloxyethoxy)ethyl acrylate alone or 2-(2-vinyloxyethoxy)ethylacrylate in combination with isobornyl acrylate, a radicalpolymerization initiator, a cationic polymerization initiator, apigment, a dispersant, and a surfactant ([0204] to [0207] of JapaneseUnexamined Patent Application Publication No. 2008-179136).

For example, Japanese Unexamined Patent Application Publication(Translation of PCT Application) No. 2008-507598 discloses a radiationcurable ink jet ink containing 25.8% by weight of hexanediol diacrylate,4.6% by weight of an amine adduct of tripropylene glycol diacrylate,2.3% by weight of 2-(2-ethoxyethoxy)ethyl acrylate, 2.5% by weight ofalkoxylated phenoxyethyl acrylate, 3.7% by weight of2-benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone, 3.2% by weight of2-hydroxy-2-methylpropiophenone, 2.8% by weight of a mixture oftrimethylbenzophenone and methylbenzophenone, 0.5% by weight ofisopropylthioxanthone, 27.8% by weight of a cyan pigment dispersionsolution, and 17.6% by weight of 2-(2-vinyloxyethoxy)ethyl acrylate([0208] and [0209] of Japanese Unexamined Patent Application Publication(Translation of PCT Application) No. 2008-507598).

For example, Japanese Patent No. 4204333 is aimed at achieving excellentactive energy ray curability of thin films and discloses a photocurablecomposition containing 47.5 parts by weight of vinyloxyethoxyethylacrylate or vinyloxyethoxyethyl methacrylate, 47.5 parts by weight of4-acryloyloxymethyl-2-methyl-2-methyl-1,3-dioxolane, 15 parts by weightof triethylene glycol diacrylate, and 5 parts by weight of aphotopolymerization initiator ([0011], [0081], and [0082] of JapanesePatent No. 4204333).

For example, Japanese Unexamined Patent Application Publication No.2010-157706 is aimed at providing an imprint curable composition whichis excellent in curability in 3 μm-thickness thin films and excellent inpattern accuracy, and discloses an imprint curable composition including15.4% by mass of a monofunctional acryl monomer, 19.3% by mass of2-(2-vinyloxyethoxy)ethyl acrylate, 51.3% by mass (total) ofbifunctional acryl monomer and trifunctional acryl monomer, 1.0% by massof a photopolymerization initiator, an antioxidant, a coupling agent,and a surfactant. ([0092] to and [0100] to [0103] of Japanese UnexaminedPatent Application Publication No. 2010-157706).

For example, Japanese Unexamined Patent Application Publication No.2009-96910 is aimed at providing an active energy ray-curable ink forink jet printing which has low viscosity at room temperature and isexcellent in flexibility of cured films, and discloses an active energyray-curable ink for ink jet printing containing 2.5 parts by weight ofpentaerythritol tetraacrylate, 32.7 parts by weight of diethylene glycolmonovinyl ether acrylate, 6 parts by weight of isobornyl acrylate, 22.7parts by weight of tetraethylene glycol diacrylate, 24.6 parts by weightof N-vinylpyrrolidone, a photopolymerization initiator, a pigment, and adispersant ([0003], [0069] to [0072], and [0077] of Japanese UnexaminedPatent Application Publication No. 2009-96910).

For example, Japanese Unexamined Patent Application Publication(Translation of PCT Application) No. 2011-500932 discloses a freeradical curable solution (INV-18) prepared by mixing 24.38% by weight ofVEEA (2-(vinylethoxy)ethyl acrylate), 53.62% by weight of SR489(tridecyl acrylate), 19.50% by weight of M600 (dipentaerythritolhexaacrylate), and 2.50% by weight of a polymerizable photoinitiatorINI-C1 (Table 18 in [0315] of Japanese Unexamined Patent ApplicationPublication (Translation of PCT Application) No. 2011-500932).

SUMMARY

However, any one of the compositions and inks disclosed in JapanesePatent Nos. 3461501 and 3544658, Japanese Unexamined Patent ApplicationPublication Nos. 2009-62541 and 2008-179136, and Japanese UnexaminedPatent Application Publication (Translation of PCT Application) No,2008-507598 has room for improvement in curability. Accordingly, anadvantage of some aspects of the invention is that it provides aphotocurable ink composition for ink jet recording which has excellentcurability.

In addition, the compositions and inks disclosed in Japanese Patent No.4204333, Japanese Unexamined Patent Application Publication Nos.2010-157706 and 2009-96910, and Japanese Unexamined Patent ApplicationPublication (Translation of PCT Application) No. 2011-500932 are poor incurability and extensibility of cured films, and cause the problem ofproducing wrinkles (hereinafter referred to as “curing wrinkles”) insurfaces of cured films, particularly when ink thick coating films ofabout 10 μm in thickness are cured. In addition, the free radicalcurable solution (INV-18) disclosed in Japanese Unexamined PatentApplication Publication (Translation of PCT Application) No. 2011-500932does not contain a colorant. A free radical curable solution and inkcomposition each containing a colorant are inferior in curability to afree radical curable solution and ink composition not each containing acolorant, and tend to be degraded in inner curability of thick films,particularly, when thick-film recording is performed. Therefore, aphotocurable ink composition for ink jet recording which contains acolorant and has excellent curability is required. Accordingly, anadvantage of some aspects of the invention is that it provides aphotocurable ink composition for ink jet recording which is excellent inthick-film curability and extensibility of cured films when thick filmsare cured, and which is capable of preventing the occurrence of curingwrinkles when thick films are cured.

The inventors conducted intensive research for resolving theabove-described problems. First, a cause for room of improvement incurability of the composition or ink disclosed in each of the patentdocuments was examined. Any one of the compositions and inks contains2-(vinyloxyethoxy)ethyl (meth)acrylate as a polymerizable compound. Itwas found that 2-(vinyloxyethoxy)ethyl (meth)acrylate has the functionof improving curability, but an ink containing only2-(vinyloxyethoxy)ethyl (meth)acrylate as a polymerizable compoundcannot be said to have sufficient curability. In other words, it wasfound that an ink containing 2-(vinyloxyethoxy)ethyl (meth)acrylate incombination with another compound as polymerizable compounds may beexcellent in curability.

Therefore, the inventors examined such another compound. First, it wasfound that each of the ink composition and the reactive diluentcomposition disclosed in Japanese Patent Nos. 3461501 and 3544658 ischaracterized by containing a compound having only a vinyl ether groupand a compound having only a (meth)acrylate group, but thesecompositions are poor in curability.

In addition, a bifunctional vinyl ether monomer (compound having only avinyl ether group as a substituent) disclosed in Japanese UnexaminedPatent Application Publication No. 2009-62541 is considered as the othercompound. However, the compound having only a vinyl ether group as asubstituent decreases a curing rate. Therefore, it was found that thebifunctional vinyl ether monomer is unsuitable as the other compound.

In addition, isobornyl acrylate disclosed in Japanese Unexamined PatentApplication Publication No. 2008-179136 is considered as the othercompound. However, isobornyl acrylate also decreases a curing rate.Therefore, it was found that isobornyl acrylate is unsuitable as theother compound.

In addition, alkoxylated phenoxyethyl acrylate disclosed in JapaneseUnexamined Patent Application Publication (Translation of PCTApplication) No. 2008-507598 is considered as the other compound.However, alkoxylated phenoxyethyl acrylate has the property ofrelatively high viscosity and relatively low solubility, and thus theradiation curable ink jet ink containing alkoxylated phenoxyethylacrylate cannot be said to have a sufficiently high curing rate.Therefore, it was found that alkoxylated phenoxyethyl acrylate isunsuitable as the other compound.

On the basis of these findings, the inventors repeated further intensiveresearch. As a result, it was found that the above-described problemscan be resolved by a photocurable ink composition for ink jet recordingwhich contains polymerizable compounds including a vinyl ethergroup-containing (meth)acrylate with a predetermined structure andphenoxyethyl (meth)acrylate, and a photopolymerization initiator,leading to the achievement of the present invention.

As a result of further intensive research for solving the problems, theinventors found that the above-described problem can be resolved by aphotocurable ink composition for ink jet recording which contains acolorant and, as polymerizable compounds, predetermined amounts of avinyl ether group-containing (meth)acrylate with a predeterminedstructure, a monofunctional (meth)acrylate other than the vinyl ethergroup-containing (meth)acrylate, and a bi- or higher-functional(meth)acrylate, leading to the achievement of the present invention.

According to an embodiment, the present invention provides thefollowing:

[1] A photocurable ink composition for ink jet recording which containspolymerizable compounds, a photopolymerization initiator, and acolorant, wherein the polymerizable compounds include a vinyl ethergroup-containing (meth)acrylate represented by general formula (I)below:

CH₂═CR¹—COOR²—O—CH═CH—R³  (I)

(wherein R¹ is a hydrogen atom or a methyl group, R² is a divalentorganic residue having 2 to 20 carbon atoms, and R³ is a hydrogen atomor a monovalent organic residue having 1 to 11 carbon atoms) andphenoxyethyl (meth)acrylate.

[2] The photocurable ink composition for ink jet recording described in[1], wherein the content of the phenoxyethyl (meth)acrylate is 9 to 60%by mass relative to the total mass of the ink composition.

[3] The photocurable ink composition for ink jet recording described in[1] or [2], wherein the photopolymerization initiator contains 7% bymass or more of an acylphosphine oxide compound relative to the totalmass of the ink composition.

[4] The photocurable ink composition for ink jet recording described in[1] or [2], wherein the photopolymerization initiator contains 7 to 15%by mass of an acylphosphine oxide compound relative to the total mass ofthe ink composition.

[5] The photocurable ink composition for ink jet recording described in[1] or [2], wherein the photopolymerization initiator contains 10 to 15%by mass of an acylphosphine oxide compound relative to the total mass ofthe ink composition.

[6] The photocurable ink composition for ink jet recording described inany one of [1] to [5], wherein the vinyl ether group-containing(meth)acrylate is 2-(vinyloxyethoxy)ethyl (meth)acrylate.

[7] The photocurable ink composition for ink jet recording described inany one of [1] to [6], wherein the content of the vinyl ethergroup-containing (meth)acrylate is 10 to 60% by mass relative to thetotal mass of the ink composition.

[8] The photocurable ink composition for ink jet recording described inany one of [1] to [7], wherein the ink composition is cured byirradiation with ultraviolet light having an emission peak wavelength ina range of 350 to 420 nm and an irradiation energy of 300 mJ/cm² orless.

[9] An ink jet recording method including an ejection step of ejectingthe photocurable ink composition for ink jet recording described in anyone of [1] to [8] onto a recording medium, and a curing step of curingthe photocurable ink composition for ink jet recording by ultravioletirradiation of the photocurable ink composition for ink jet recordingejected in the ejection step.

According to a second embodiment, the present invention provides thefollowing:

[1] A photocurable ink composition for ink jet recording which containspolymerizable compounds, a photopolymerization initiator, and acolorant, wherein the polymerizable compounds include, relative to thetotal mass of the ink composition, 10 to 40% by mass of a vinyl ethergroup-containing (meth)acrylate represented by general formula (I)below:

CH₂═CR¹—COOR²—O—CH═CH—R³  (I)

(wherein R¹ is a hydrogen atom or a methyl group, R² is a divalentorganic residue having 2 to 20 carbon atoms, and R³ is a hydrogen atomor a monovalent organic residue having 1 to 11 carbon atoms), 20 to 60%by mass of a monofunctional (meth)acrylate (excluding the vinyl ethergroup-containing (meth)acrylate), and 10 to 40% by mass of apolyfunctional (meth)acrylate.

[2] The photocurable ink composition for ink jet recording described in[1], wherein the monofunctional (meth)acrylate contains 10 to 60% bymass of phenoxyethyl (meth)acrylate relative to the total mass of theink composition.

[3] The photocurable ink composition for ink jet recording described in[1] or [2], wherein the photopolymerization initiator contains 6 to 13%by mass of an acylphosphine oxide compound relative to the total mass ofthe ink composition.

[4] The photocurable ink composition for ink jet recording described inany one of [1] to [3], wherein the content of the monofunctional(meth)acrylate is 20 to 40% by mass relative to the total mass of theink composition.

[5] The photocurable ink composition for ink jet recording described inany one of [1] to [4], wherein the content of the polyfunctional(meth)acrylate is 20 to 30% by mass relative to the total mass of theink composition.

[6] The photocurable ink composition for ink jet recording described inany one of [1] to [5], wherein the ink composition can be cured byirradiation with ultraviolet light having an emission peak wavelength ina range of 350 to 420 nm and an irradiation energy of 300 mJ/cm² orless.

[7] The photocurable ink composition for ink jet recording described inany one of [1] to [6], wherein the vinyl ether group-containing(meth)acrylate is 2-(vinyloxyethoxy)ethyl (meth)acrylate.

[8] The photocurable ink composition for ink jet recording described inany one of [1] to [7], wherein the primary skin irritation index of themonofunctional (meth)acrylate is 0 to 4.

[9] An ink jet recording method using the photocurable ink compositionfor ink jet recording described in any one of [1] to [8], the methodincluding causing the photocurable ink composition for ink jet recordingto adhere to a recording medium; and irradiating, using a light-emittingdiode, the adhering photocurable ink composition for ink jet recordingwith ultraviolet light having an emission peak wavelength in a range of350 to 420 nm.

[10] The ink jet recording method described in [9], wherein theirradiation energy of the ultraviolet light is 300 mJ/cm² or less.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A first embodiment of the present invention is described in detailbelow. The present invention is not limited to this embodiment and canbe carried out with various changes within the scope of the gist of theinvention.

In the specification, the term “curing” represents that an inkcontaining a polymerizable compound is solidified by polymerization ofthe polymerizable compound when the ink is irradiated with light. Theterm “curability” refers to the property of being cured in response tolight. The term “adhesion” refers to the property that a coated film islittle separated from a base. The term “abrasion resistance” refers tothe property that a cured product is little separated from a recordingmedium by scratching.

In the specification, the term “(meth)acrylate” represents at least oneof acrylate and corresponding methacrylate, and the term “(meth)acryl”represents at least one of acryl and corresponding methacryl.

In the specification, a “recorded material” represents a material onwhich a cured product is formed by recording an ink on a recordingmedium. In the specification, the cured product represents a curedmaterial including an ink cured film or coating film.

[Photocurable Ink Composition for Ink Jet Recording]

A photocurable ink composition for ink jet recording (simply referred toas an “ink composition” hereinafter) according to an embodiment of thepresent invention contains polymerizable compounds, aphotopolymerization initiator, and a colorant. The polymerizablecompounds include a vinyl ether group-containing (meth)acrylaterepresented by general formula (I):

CH₂═CR¹—COOR²—O—CH═CH—R³  (I)

(wherein R¹ is a hydrogen atom or a methyl group, R² is a divalentorganic residue having 2 to 20 carbon atoms, and R³ is a hydrogen atomor a monovalent organic residue having 1 to 11 carbon atoms) andphenoxyethyl (meth)acrylate.

Hereinafter, additives (components) which are contained or can becontained in the ink composition according to the embodiment aredescribed.

[Polymerizable Compound]

The polymerizable compounds contained in the ink composition accordingto the embodiment are capable of curing an printed ink by polymerizationcaused by the action of the photopolymerization initiator describedbelow during ultraviolet irradiation.

(Vinyl Ether Group-Containing (Meth)Acrylate)

The vinyl ether group-containing (meth)acrylate contained as anessential polymerizable compound in the embodiment is represented by thegeneral formula (I).

The ink composition contains the vinyl ether group-containing(meth)acrylate in combination with the phenoxyethyl (meth)acrylatedescribed below. Therefore, the ink can be decreased in viscosity, andany one of curability, abrasion resistance, adhesion, and solubility ofthe photopolymerization initiator can be improved. The cause for theexcellent solubility of the photopolymerization initiator is improvedcompatibility between the polymerizable compounds and the additives suchas the photopolymerization initiator.

Furthermore, when a compound containing both a vinyl ether group and a(meth)acrylate group in its molecule is used, ink curability isdesirably more improved as compared with when a vinyl ethergroup-containing compound and a compound containing a (meth)acrylategroup (one of radical polymerizable groups) are separated used.

In the general formula (I), a divalent organic residue represented by R²and having 2 to 20 carbon atoms is preferably a linear, branched, orcyclic alkylene group which has 2 to 20 carbon atoms and may besubstituted, an alkylene group which has 2 to 20 carbon atoms and anoxygen atom through an ether bond and/or an ester bond in its structureand which may be substituted, or a divalent aromatic group which has 6to 11 carbon atoms and may be substituted. Preferred specific examplesof these groups include alkylene groups having 2 to 6 carbon atoms, suchas an ethylene group, a n-propylene group, an isopropylene group, abutylene group, and the like; and alkylene groups having 2 to 9 carbonatoms and an oxygen atom through an ether bond in its structure, such asan oxyethylene group, an oxy-n-propylene group, an oxyisopropylenegroup, and an oxybutylene group, and the like.

In the general formula (I), a monovalent organic residue represented byR³ and having 1 to 11 carbon atoms is preferably a linear, branched, orcyclic alkyl group which has 1 to 10 carbon atoms and may besubstituted, or an aromatic group which has 6 to 11 carbon atoms and maybe substituted. Preferred examples of these groups include alkyl groupshaving 1 to 2 carbon atoms, such as a methyl group and an ethyl group,and aromatic groups having 6 to 8 carbon atoms, such as a phenyl groupand a benzyl group.

When each of the organic residues is a group which may be substituted,substituents are divided into groups containing a carbon atom and groupsnot containing a carbon atom. When the substituent is a group containinga carbon atom, the carbon atom is counted in the number of carbon atomsof the organic residue. Examples of the group containing a carbon atominclude, but are not limited to, a carboxyl group and an alkoxy group.Examples of the group not containing a carbon atom include, but are notlimited to, a hydroxyl group and a halo-group.

Examples of the vinyl ether group-containing (meth)acrylate include, butare not limited to, 2-vinyloxyethyl (meth)acrylate, 3-vinyloxypropyl(meth)acrylate, 1-methyl-2-vinyloxyethyl (meth)acrylate,2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl (meth)acrylate,1-methyl-3-vinyloxypropyl (meth)acrylate, 1-vinyloxymethylpropyl(meth)acrylate, 2-methyl-3-vinyloxypropyl (meth)acrylate,1,1-dimethyl-2-vinyloxyethyl (meth)acrylate, 3-vinyloxybutyl(meth)acrylate, 1-methyl-2-vinyloxypropyl (meth)acrylate,2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl (meth)acrylate,6-vinyloxyhexyl (meth)acrylate, 4-vinyloxymethylcyclohexylmethyl(meth)acrylate, 3-vinyloxymethylcyclohexylmethyl (meth)acrylate,2-vinyloxymethylcyclohexylmethyl (meth)acrylate,p-vinyloxymethylphenylmethyl (meth)acrylate,m-vinyloxymethylphenylmethyl (meth)acrylate,o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl(meth)acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyethoxy) propyl (meth)acrylate, 2-(vinyloxyethoxy) isopropyl(meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxy) isopropyl (meth)acrylate,2-(vinyloxyethoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyethoxy) propyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyethoxyethoxy) isopropyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)isopropyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,polyethylene glycol monovinyl ether (meth)acrylate, and polypropyleneglycol monovinyl ether (meth)acrylate.

Among these, 2-(vinyloxyethoxy)ethyl (meth)acrylate, i.e., at least oneof 2-(vinyloxyethoxy)ethyl acrylate and 2-(vinyloxyethoxy)ethylmethacrylate, is preferred, and 2-(vinyloxyethoxy)ethyl acrylate is morepreferred because when it is used in combination with the phenoxyethyl(meth)acrylate described below, the ink can be decreased in viscosityand has a high flashing point and more excellent curability. Inparticular, any one of 2-(vinyloxyethoxy)ethyl acrylate and2-(vinyloxyethoxy)ethyl methacrylate has a simple structure and a lowmolecular weight, and thus the viscosity of the ink can be furtherdecreased. Examples of 2-(vinyloxyethoxy)ethyl (meth)acrylate include2-(2-vinyloxyethoxy)ethyl (meth)acrylate and 2-(1-vinyloxyethoxy)ethyl(meth)acrylate. Examples of 2-(vinyloxyethoxy)ethyl acrylate include2-(2-vinyloxyethoxy)ethyl acrylate and 2-(1-vinyloxyethoxy)ethylacrylate. In addition, 2-(vinyloxyethoxy)ethyl acrylate is superior incurability to 2-(vinyloxyethoxy)ethyl methacrylate.

These vinyl ether group-containing (meth)acrylates may be used alone orin combination of tow or more.

The content of the vinyl ether group-containing (meth)acrylate ispreferably 10 to 60% by mass relative to the total mass (100% by mass)of the ink composition in order to further improve curability, and morepreferably 10 to 30% by mass and still more preferably 20 to 30% by massin order to further improve abrasion resistance and adhesion in additionto curability. On the other hand, in order that the ink composition hasparticularly excellent curability, the content is more preferably 20 to60% by mass and still more preferably 30 to 60% by mass.

Examples of a method for producing the vinyl ether group-containing(meth)acrylate include, but are not limited to, a method (method B) ofesterifying (meth)acrylic acid with hydroxyl group-containing vinylether, a method (method C) of esterifying (meth)acrylic acid halide withhydroxyl group-containing vinyl ether, a method (method D) ofesterifying (meth)acrylic anhydride with hydroxyl group-containing vinylether, a method (method E) of ester-exchanging (meth)acrylate withhydroxyl group-containing vinyl ether, a method (method F) ofesterifying (meth)acrylic acid with halogen-containing vinyl ether, amethod (method G) of esterifying (meth)acrylic acid alkali (earth) metalsalt with halogen-containing vinyl ether, a method (method H) ofvinyl-exchanging hydroxyl group-containing (meth)acrylate with vinylcarboxylate, and a method (method I) of ether-exchanging hydroxylgroup-containing (meth)acrylate with alkyl vinyl ether.

Among these, the method E is preferred because a desired effect can bemore exhibited in the embodiment.

(Phenoxyethyl (Meth)Acrylate)

The ink composition according to the embodiment contains thephenoxyethyl (meth)acrylate as the polymerizable compound. Since the inkcomposition according to the embodiment contains the phenoxyethyl(meth)acrylate as the polymerizable compound in addition to the vinylether group-containing (meth)acrylate, the ink can be decreased inviscosity, and all of curability, abrasion resistance, adhesion, andphotopolymerization initiator solubility can be improved.

In order to further improve curability, the content of the phenoxyethyl(meth)acrylate is preferably 9 to 60% by mass, more preferably 10 to 50%by mass, and still more preferably 10 to 40% by mass relative to thetotal mass (100% by mass) of the ink composition. When the content isnot less than the lower limit value (particularly 10% by mass), thesolubility of the photopolymerization initiator, in addition tocurability, can be further improved. On the other hand, when the contentis not more than the upper limit value (particularly 50% by mass),adhesion, in addition to curability, can be further improved.

(Monofunctional (Meth)Acrylate)

The ink composition according to the embodiment may further contain themonofunctional (meth)acrylate (excluding the phenoxyethyl(meth)acrylate) as the polymerizable compound. Examples thereof include,but are not limited to, isoamyl (meth)acrylate, stearyl (meth)acrylate,lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate,isomyristyl (meth)acrylate, isostearyl (meth)acrylate,2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate,4-hydroxybutyl (meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxy diethylene glycol(meth)acrylate, methoxy polyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate,isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate,lactone-modified flexible (meth)acrylate, tert-butylcyclohexyl(meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl(meth)acrylate, benzyl (meth)acrylate, ethoxylated nonylphenyl(meth)acrylate, alkoxylated nonylphenyl (meth)acrylate, andp-cumylphenol EO (ethylene oxide)-modified (meth)acrylate.

These monofunctional (meth)acrylates may be used alone or in combinationof two or more.

The ink composition preferably contains the monofunctional(meth)acrylate within a range in which the desired effect of theembodiment is not impaired. The content of the monofunctional(meth)acrylate is preferably 50% by mass or less relative to the totalmass (100% by mass) of the ink composition.

(Polyfunctional (Meth)Acrylate)

The ink composition according to the embodiment may further contain thepolyfunctional (meth)acrylate as the polymerizable compound. Examples ofa bifunctional (meth)acrylate (excluding the predetermined vinyl ethergroup-containing (meth)acrylate) as the polyfunctional (meth)acrylateinclude, hut are not limited to, triethylene glycol di(meth)acrylate,tetraethylene glycol di(meth)acrylate, polyethylene glycoldi(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropyleneglycol di(meth)acrylate, polypropylene glycol di(meth)acrylate,1,4-dutanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate,dimethyloltricyclodecane di(meth)acrylate, bisphenol A EO (ethyleneoxide) adduct di(meth)acrylate, bisphenol A PO (propylene oxide) adductdi(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate, andpolytetramethylene glycol di(meth)acrylate. Among these, at least one ofdipropylene glycol diacrylate and tripropylene glycol diacrylate ispreferred because of high curability and easy decrease in viscosity ofthe ink.

Examples of a tri- or higher-functional (meth)acrylate as thepolyfunctional (meth)acrylate include, but are not limited to,trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropanetri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate,ditrimethylolpropane tetra(meth)acrylate, glyceryl propoxytri(meth)acrylate, caprolactone-modified trimethylolpropanetri(meth)acrylate, pentaerythritolethoxy tetra(meth)acrylate, andcaprolactam-modified dipentaerythritol hexa(meth)acrylate.

These polyfunctional (meth)acrylates may be used alone or in combinationof two or more.

The ink composition preferably contains the polyfunctional(meth)acrylate within a range in which the desired effect of theembodiment is not impaired. The content of the polyfunctional(meth)acrylate is preferably 40% by mass or less relative to the totalmass (100% by mass) of the ink composition. When the content of thepolyfunctional (meth)acrylate falls in the above-described range, anincrease in viscosity of the ink can be prevented, and good flexibilityof a recorded material can be secured.

(Polymerizable Compound Other than the Above)

Besides the vinyl ether group-containing (meth)acrylate, themonofunctional (meth)acrylate, and the polyfunctional (meth)acrylate,any one of various known monofunctional and polyfunctional monomers andoligomers can be further used (hereinafter, referred to as the “otherpolymerizable compound”). Examples of the monomers include unsaturatedcarboxylic acids such as itaconic acid, crotonic acid, isocrotonic acid,maleic acid, and the like, salts or esters thereof, urethane, amides andanhydrides thereof, acrylonitrile, styrene, various unsaturatedpolyesters, unsaturated polyethers, unsaturated polyamides, andunsaturated urethanes. Examples of the oligomers include oligomerscomposed of the monomers.

These other polymerizable compounds may be used alone or in combinationof two or more.

The ink composition preferably contains the other polymerizable compoundwithin a range in which the desired effect of the embodiment is notimpaired. The content of the other polymerizable compound is preferably10% by mass or less relative to the total mass (100% by mass) of the inkcomposition.

[Photopolymerization Initiator]

The photopolymerization initiator contained in the ink compositionaccording to the embodiment is used for curing an ink present on asurface of a recording medium by photopolymerization under ultravioletirradiation to form a print. Among radiations, the use of ultravioletrays (UV) exhibits excellent safety and can suppress the cost of a lightsource lamp. The photopolymerization initiator is not limited as long asactive species such as radical or cation are produced by light(ultraviolet ray) energy to initiate polymerization of the polymerizablecompounds. However, a photo-radical polymerization initiator and aphoto-cationic polymerization initiator can be used, and particularly,the photo-radical polymerization initiator is preferably used.

Examples of the photo-radical polymerization initiator include aromaticketones, acylphosphine oxide compounds, aromatic onium salt compounds,organic peroxides, thio compounds (thioxanthone compounds, thiophenylgroup-containing compounds, and the like), hexaaryl biimidazolecompounds, ketoxime ester compounds, borate compounds, aziniumcompounds, metallocene compounds, active ester compounds, compoundshaving carbon-halogen bonds, and alkylamine compounds.

Among these, at least one of the acylphosphine oxide compounds and thethioxanthone compounds is preferably used, the acylphosphine oxidecompounds are more preferably used, and the acylphosphine oxidecompounds are still more preferably used in combination with thethioxanthone compounds, particularly, because the curability of an inkcan be further improved.

Examples of the photo-radical polymerization initiator includeacetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenylketone, 2,2-dimethoxy-2-phenyl acetophenone, xanthone, fluorenone,benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole,3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone,4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether,benzoin ethyl ether, benzyl dimethyl ketal,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one,2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone,diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide,2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide,2,4-diethylthioxanthone, andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide.

Examples of commercial products of the photo-radical polymerizationinitiator include IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethan-1-one),IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173(2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959(1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one),IRGACURE 127(2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl]-2-methyl-propan-1-one},IRGACURE 907 (2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one),IRGACURE 369(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1), IRGACURE379(2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone),DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), IRGACURE 784(bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium),IRGACURE OXE 01 (1.2-octanedione, 1-[4-(phenylthio)-,2-(O-benzoyloxime)]), IRGACURE OXE 02 (ethanone,1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime)),and IRGACURE 754 (mixture of oxyphenylacetic acid,2-[2-oxo-2-phenylacetoxyethoxy]ethyl ester and oxyphenylacetic acid, and2-(2-hydroxyethoxy)ethyl ester) (trade names, manufactured by BASFCorporation), KAYACURE DETX-S (2,4-diethylthioxanthone) (trade name,manufactured by Nippon Kayaku Co., Ltd.), Speedcure TPO(2,4,6-trimethylbenzoyldiphenyl-phosphine oxide) and Speedcure DETX(2,4-diethylthioxanthen-9-one) (trade name, manufactured by LambsonLtd.), Lucirin TPO, LR8893, and LR8970 (trade names, manufactured byBASF Corporation), and UBECRYL P36 (trade name, manufactured by UCBCorporation).

These photopolymerization initiators may be used alone or in combinationof two or more.

The content of the photopolymerization initiator is preferably 8 to 20%by mass relative to the total mass (100% by mass) of the ink compositionin order to achieve the excellent curability by improving theultraviolet curing rate and to avoid coloring due to thephotopolymerization initiator and the photopolymerization initiator fromremaining undissolved.

In particular, when the photopolymerization initiator contains anacylphosphine oxide compound, the content of the acylphosphine oxidecompound is preferably 7% by mass or more, more preferably 7 to 15% bymass, particularly preferably 10 to 15% by mass, and still morepreferably 10 to 14% by mass, relative to the total mass (100% by mass)of the ink composition. When the content is not less than the lowerlimit (particularly, 10% by mass), the curability is more excellent.More specifically, the curability is more excellent because asatisfactory curing rate can be achieved by curing with LED (preferably,emission peak wavelength: 350 nm to 420 nm). On the other hand, when thecontent is not more than the upper limit (particularly, 14% by mass),the solubility of the photopolymerization initiator is more excellent.

In addition, when the content of the acylphosphine oxide compound fallsin the above-described range, the acylphosphine oxide compound maypreferably contain 4% by mass or more, more preferably 6% by mass ormore, of a bisacylphosphine oxide compound relative to the total mass(100% by mass) of the ink composition. When the content of thebisacylphosphine oxide compound is not less than the lower limit(particularly, 6% by mass), the curability is more excellent. Further,the upper limit of the content of the bisacylphosphine oxide compound ispreferably 10% by mass or less, more preferably 8% by mass or less,relative to the total mass (100% by mass) of the ink composition becauseof the more excellent solubility of the initiator.

In addition, when the content of the acylphosphine oxide compound fallsin the above-described range, the acylphosphine oxide compound maypreferably contain 53% by mass or more, more preferably 55% by mass ormore, of a bisacylphosphine oxide compound relative to the total mass(100% by mass) of the acylphosphine oxide compound. When the content ofthe bisacylphosphine oxide compound is not less than the lower limit(particularly, 55% by mass), the curability is more excellent. Further,the upper limit of the content of the bisacylphosphine oxide compound ispreferably 90% by mass or less, more preferably 80% by mass or less,relative to the total mass (100% by mass) of the acylphosphine oxidecompound because the more excellent solubility of the initiator.

Examples of the bisacylphosphine oxide compound include, but are notlimited to, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide andbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. Examplesof the arylphosphine oxide compound other than the bisacylphosphineoxide compound include, but are not limited to, monoacylphosphine oxidecompounds. Examples of the monoacylphosphine oxide compounds include,but are not limited to, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide.

Further, when the content of the phenoxyethyl (meth)acrylate falls inthe above-described preferred range, the solubility of the acylphosphineoxide compound is further improved, and thus the content of theacylphosphine oxide compound can be adjusted in the above-describedpreferred range. Therefore, a correlation is established between thecontents of the phenoxyethyl (meth)acrylate and the acylphosphine oxidecompound.

When the photopolymerization initiator contains a thioxanthone compound,the content thereof is preferably 1 to 5% by mass relative to the totalmass (100% by mass) of the ink composition.

[Colorant]

The ink composition according to the embodiment further contains thecolorant. As the colorant, at least one of a pigment and a dye can beused, and a pigment is preferred in view of excellent light resistance.

(Pigment)

In the embodiment, the light resistance of the ink composition can beimproved by using a pigment as the colorant. As the pigment, either aninorganic pigment or an organic pigment can be used.

Usable examples of the inorganic pigment include carbon black (C. I.Pigment Black 7) such as furnace black, lamp black, acetylene black,channel black, and the like, iron oxide, and titanium oxide.

Usable examples of the organic pigment include azo pigments such asinsoluble azo pigments, condensed azo pigments, azo-lakes, chelate azopigments, and the like; polycyclic pigments such as phthalocyaninepigments, perylene and perynone pigments, anthraquinone pigments,quinacridone pigments, dioxane pigments, thioindigo pigments,isoindolinone pigments, quinophthalone pigments, and the like; dyechelates (e.g., basic dye-type chelates, acid dye-type chelates, and thelike), dye lakes (basic dye-type lakes and acid dye-type lakes), nitropigments, nitroso pigments, aniline black, and daylight fluorescentpigments.

In further detail, examples of carbon black used as a black ink includeNo. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8,MA100, No. 2200B, and the like (trade names, manufactured by MitsubishiChemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500,Raven 1255, Raven 700, and the like (trade names, manufactured by CarbonColumbia Corporation), Regal 400R, Regal 330R, Regal 660R, Mogul L,Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000,Monarch 1100, Monarch 1300, Monarch 1400, and the like (trade names,manufactured by CABOT JAPAN K.K.), and Color Black FW1, Color Black FW2,Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150,Color Black S160, Color Black S170, Printex 35, Printex U, Printex V,Printex 140U, Special Black 6, Special Black 5, Special Black 4A,Special Black 4, and the like (trade names, manufactured by DegussaCorporation).

Examples of a pigment used as a white ink include C. I. Pigment White 6,18, and 21.

Examples of a pigment used as a yellow ink include C. I. Pigment Yellow1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55,65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114,117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172,and 180.

Examples of a pigment used as a magenta ink include C. I. Pigment Red 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23,30, 31, 32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 88,112, 114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176,177, 178, 179, 184, 185, 187, 202, 209, 219, 224, and 245, and C. I.Pigment Violet 19, 23, 32, 33, 36, 38, 43, and 50.

Examples of a pigment used as a cyan ink include C. I. Pigment Blue 1,2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, and 66,and C. I. Vat Blue 4 and 60.

Examples of pigments other than magenta, cyan, yellow include C. I.Pigment Green 7 and 10, C. I. Pigment Brown 3, 5, 25, and 26, C. I.Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, and63.

These pigments may be used alone or in combination of two or more.

(Dye)

In the embodiment, a dye can be used as the colorant. The dye is notparticularly limited, and an acid dye, a direct dye, a reactive dye, anda basic dye can be used. Examples of the dye include C. I. Acid Yellow17, 23, 42, 44, 79, and 142, C. I. Acid Red 52, 80, 82, 249, 254, and289, C. I. Acid Blue 9, 45, and 249, C. I. Acid Black 1, 2, 24, and 94,C. I. Food Black 1 and 2, C. I. Direct Yellow 1, 12, 24, 33, 50, 55, 58,86, 132, 142, 144, and 173, C. I. Direct Red 1, 4, 9, 80, 81, 225, and227, C. I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, and 202, C.I. Direct Black 19, 38, 51, 71, 154, 168, 171, and 195, C. I. ReactiveRed 14, 32, 55, 79, and 249, and C. I. Reactive Black 3, 4, and 35.

These dyes may be used alone or in combination of two or more.

The content of the colorant is preferably 1 to 20% by mass relative tothe total mass (100% by mass) of the ink composition because goodcoloring properties can be exhibited, and the inhibition of curing of acoating film due to light absorption by the colorant can be decreased. Aphotocurable ink composition containing a colorant is inferior to an inkcomposition not containing a colorant in curability and adhesion andabrasion resistance of a recorded material. However, the photocurableink composition according to the embodiment has excellent curability,adhesion, and abrasion resistance and can be used for image recording.

[Dispersant]

When the ink composition according to the embodiment contains a pigment,the ink composition may further contain a dispersant for improvingpigment dispersibility. Examples of the dispersant include, but are notlimited to, dispersants such as polymeric dispersants commonly used forpreparing pigment dispersion solutions. Specific examples of thepolymeric dispersants include those each containing, as a maincomponent, at least one of polyoxyalkylene polyalkylene polyamines,vinyl polymers and copolymers, acryl polymers and copolymers,polyesters, polyamides, polyimides, polyurethanes, amino polymers,silicon-containing polymers, sulfur-containing polymers,fluorine-containing polymers, and epoxy resins. Commercial products ofthe polymeric dispersants include Ajisper Series (trade name)manufactured by Ajinomoto Fine-Techno Co., Inc., Solsperse Series(Solsperse 32000, 36000, etc. (trade name)) available from Avecia Co.,Disperbyk Series (trade name) manufactured by BYK Chemie Co., Ltd., andDisparlon Series (trade name) manufactured by Kusumoto Chemical Ltd.

These dispersants may be used alone or in combination of two or more.The content of the dispersant is not particularly limited, and thedispersant may be added in an appropriate desired amount.

[Polymerization Inhibitor]

The ink composition according to the embodiment may further contain apolymerization inhibitor. When the ink composition contains thepolymerization inhibitor, polymerization reaction of the polymerizablecompounds can be prevented before curing.

The polymerization inhibitor is not particularly limited, but, forexample, a phenolic polymerization inhibitor can be used. Examples ofthe phenolic polymerization inhibitor include, but are not limited to,

p-methoxyphenol, cresol, tert-butylcatechol, di-tert-butyl-para-cresol,hydroquinone monomethyl ether, α-naphthol,3,5-di-tert-butyl-4-hydroxytoluene, 2,6-di-tert-butyl-4-methylphenol,2,2′-methylene-bis(4-methyl-6-tert-butylphenol),2,2′-methylene-bis(4-ethyl-6-butylphenol), and4,4′-thio-bis(3-methyl-6-tert-butylphenol).

Examples of commercial products of the phenolic polymerization inhibitorinclude p-Methoxyphenol (trade name, manufactured by Tokyo ChemicalIndustry Co., Ltd., p-methoxyphenol), Nonflex MBP (trade name,manufactured by Seiko Chemical Co., Ltd.,2,2′-methylene-bis(4-methyl-6-tert-butylphenol)), and BHT Swanox (tradename, manufactured by Seiko Chemical Co., Ltd.,2,6-di-tert-butyl-4-methylphenol)).

These polymerization inhibitors may be used alone or in combination oftwo or more. The content of the polymerization inhibitor is notparticularly limited, and the polymerization inhibitor may be added inan appropriate desired amount.

[Slipping Agent]

The ink composition according to the embodiment may further contain aslipping agent (surfactant). The slipping agent is not particularlylimited, but, for example, a polyester-modified silicone orpolyether-modified silicone can be used as a silicone surfactant, andparticularly, polyether-modified polydimethylsiloxane orpolyester-modified polydimethylsiloxane can be preferably used. Examplesof commercial products of the slipping agent include BYK-347, BYK-348,and BYK-UV3500, 3510, 3530, and 3570 (above manufactured by BYK Co.,Ltd.).

These slipping agents may be used alone or in combination of two ormore. The content of the slipping agent is not particularly limited, andthe slipping agent may be added in an appropriate desired amount.

[Other Additives]

The ink composition according to the embodiment may further containadditives (components) other than the above-described additives. Thesecomponents are not particularly limited, but, for example, a generallyknown polymerization accelerator, permeation accelerator, and wettingagent (humectant), and other additives can be used. Examples of theother additives include a generally known fixing agent, fungicide,antiseptic, antioxidant, ultraviolet absorber, chelating agent, pHadjuster, and thickener.

[Characteristics of Photocurable Ink Composition for Ink Jet Recording]

The viscosity at 25° C. of the ink composition is preferably less than35 mPa·s and more preferably 25 mPa·s or less in order to improveejection stability of the ink and further improve curability of the ink.

In addition, the ink composition is preferably cured by irradiation withultraviolet light having an emission peak wavelength within the range of350 to 420 nm. When the ink composition of the embodiment can be curedat an emission peak wavelength within the above-described range, the inkcomposition can be rapidly cured with low energy due to the composition.In particular, the possibility of curing with low energy preferablyleads to the possibility of using a light-emitting diode (LED), whichhas recently attracted attention from the environmental viewpoint, as anultraviolet irradiation source. That is, the ink composition of theembodiment of the present invention is excellent in curability with LED.

In addition, the ink composition is preferably cured with an ultravioletirradiation energy of 300 mJ/cm² or less, and more preferably 200 mJ/cm²or less. By using the ink composition, an image can be formed at lowcost. The irradiation energy is calculated by multiplying theirradiation time by the irradiation intensity.

According to the embodiment, it is possible to provide the photocurableink composition for ink jet recording which has excellent curability,low viscosity, excellent adhesion and abrasion resistance of an image(cured product), and excellent solubility of the photopolymerizationinitiator.

[Recording Medium]

The ink composition according to the embodiment of the present inventionis ejected on a recording medium to form a recorded material by an inkjet recording method described below. As the recording medium, forexample, an absorbent or non-absorbent recording medium can be used. Theink jet recording method according to an embodiment described below canbe widely applied to recording media having various absorptionperformances, ranging from a non-absorbent recording medium which anaqueous ink hardly permeates to an absorbent recording medium which anaqueous ink easily permeates. However, when the ink composition isapplied to the non-absorbent recording medium, a drying step may berequired after curing by ultraviolet irradiation.

Examples of the absorbent recording medium include, but are not limitedto, plain paper such as electrophotographic paper with high permeabilityto aqueous ink, ink jet paper (ink jet exclusive paper provided with anink-absorbing layer composed of silica particles or alumina particles oran ink-absorbing layer composed of a hydrophilic polymer such aspolyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), or the like), andart paper, coated paper, cast paper, and the like which have relativelylow permeability to aqueous ink and are used for general offsetprinting.

Examples of the non-absorbent recording medium include, but are notlimited to, plastic films, sheets, and plates of polyvinyl chloride(PVC), polyethylene, polypropylene, polyethylene terephthalate (PET),and the like; metal plates of iron, silver, copper, aluminum, and thelike; metal plates and plastic films produced by vapor-depositing anyone of the metals; alloy plates of stainless, brass, and the like.

[Ink Jet Recording Method]

An embodiment of the present invention relates to an ink jet recordingmethod. The photocurable ink composition for ink jet recording accordingto the above-described embodiment of the present invention can bepreferably used in the ink jet recording method according to theembodiment. The ink jet recording method of the embodiment includes anejection step of ejecting the ink composition on a recording medium, anda curing step of curing the ink composition by ultraviolet irradiationof the ink composition ejected in the ejection step. Consequently, animage, i.e., a coating film (cured film), is formed from the inkcomposition cured on the recording medium. In addition, anotherembodiment of the present invention relates to the photocurable inkcomposition for ink jet recording according to the above-describedembodiment of the present invention which is used in the ink jetrecording method according to an embodiment of the present invention.The photocurable ink composition for ink jet recording according to theembodiment of the present invention which is used in the ink jetrecording method according to an embodiment of the present inventionrepresents the photocurable ink composition for ink jet recordingaccording to the embodiment of the present invention which is sold for arecording apparatus for recording by the ink jet recording methodaccording to an embodiment of the present invention.

[Ejection Step]

In the ejection step, the ink composition is ejected on the recordingmedium and adheres to the recording medium. The viscosity of the inkcomposition during ejection is preferably 3 to 20 mPa·s. When theviscosity of the ink composition is this value under a condition wherethe ink composition is at room temperature or is not heated, the inkcomposition may be ejected at room temperature or without heating. Inthis case, the ink temperature during ejection is preferably 20 to 30°C. On the other hand, the ink composition may be ejected with desiredviscosity by heating to a predetermined temperature. In this way, goodejection stability can be realized.

The photocurable ink composition for ink jet recording of the embodimentof the present invention has higher viscosity than that of a usualaqueous ink composition and thus causes a large change in viscosity witha temperature change during ejection. Such a change in viscosity of theink greatly influences a change in droplet size and a change in dropletejection rate, resulting in deterioration in image quality. Therefore,the temperature of ink during ejection is preferably maintained asconstant as possible.

[Curing Step]

In the next curing step, the ink composition ejected and adhering to therecording medium is cured by light (ultraviolet light) irradiation. Thisis because the photopolymerization initiator contained in the inkcomposition is decomposed by ultraviolet irradiation to produceinitiation species such as radical, acid, and base, thereby acceleratingpolymerization reaction of the polymerizable compounds by the functionof the initiation species. Alternatively, the polymerization reaction ofthe polymerizable compounds is initiated by ultraviolet irradiation. Inthis case, when a sensitizing dye is present together with thephotopolymerization initiator in the ink composition, the sensitizingdye in the system comes into an excited state by absorbing ultravioletlight, and decomposition of the photopolymerization initiator isaccelerated by contact with the photopolymerization initiator, so thathigh-sensitivity curing reaction can be achieved.

A mercury lamp, a gas/solid-state laser, and the like are mainly used asultraviolet sources, and a mercury lamp and a metal halide lamp arewidely known as light sources used for curing photocurable inkcompositions for ink jet recording. On the other hand, at present, amercury-free type is strongly demanded from the viewpoint ofenvironmental protection, and the replacement by a GaN-basedsemiconductor ultraviolet light-emitting device is very useful from theindustrial and environmental viewpoint. Further, a ultravioletlight-emitting diode (UV-LED) and an ultraviolet laser diode (UV-LD)have a small size, long life, high efficiency, and low cost, and arethus expected as light sources for photocurable ink jet. In particular,UV-LED is preferred.

In addition, the photocurable ink composition for ink jet recordingwhich can be preferably cured with an irradiation energy of 300 mJ/cm²or less is preferably used in the ink jet recording method using aUV-LED preferably having an emission peak wavelength within the range of350 to 420 nm because the output of LED can be easily increased. In thiscase, low-cost printing and a high printing speed can be realized. Suchan ink composition can be produced by containing at least one of thephotopolymerization initiator which is decomposed by irradiation withultraviolet light within the above-described wavelength range and thepolymerizable compound which is initiated to be polymerized byirradiation with ultraviolet light within the above-described wavelengthrange.

In addition, curing is preferably performed using a UV-LED with a peakirradiation intensity of 800 mW/cm² or more, and more preferably a peakintensity of 800 to 2000 mW/cm². In this case, curability of the inkcomposition can be further improved, and the appearance of a recordedmaterial can also be improved.

According to the embodiment, it is possible to provide the preferred inkjet recording method using the photocurable ink composition for ink jetrecording which has excellent curability, low viscosity, excellentadhesion and abrasion resistance of an image (cured product), andexcellent solubility of the photopolymerization initiator.

A second embodiment of the present invention is described in detailbelow. The present invention is not limited to this embodiment describedbelow and can be carried out with various changes within the scope ofthe gist of the invention.

In the specification, the term “curing” represents that an inkcontaining a polymerizable compound is solidified by polymerization ofthe polymerizable compound when the ink is irradiated with light. Theterm “curability” refers to the property of being cured in response tolight. The term “extensibility”, otherwise referred to as “elongation ofan ink cured film (coating film)”, refers to the property that a curedfilm is extended without cracking when a recorded material formed bycuring an ink coating film is stretched.

In the specification, “(meth)acrylate” represents at least one ofacrylate and corresponding methacrylate, “(meth)acryl” represents atleast one of acryl and corresponding methacryl, and “(meth)acryloyl”represents at least one of acryloyl and corresponding methacryloyl.

In the specification, the term “recorded material” represents a materialon which an ink is recorded to form a cured product by recording an inkon a recording medium. In the specification, the cured productrepresents a cured material including an ink cured film or coated film.

[Photocurable Ink Composition for Ink Jet Recording]

A photocurable ink composition for ink jet recording (simply referred toas an “ink composition” hereinafter) according to an embodiment of thepresent invention contains polymerizable compounds and aphotopolymerization initiator. The polymerizable compounds include,relative to the total mass (100% by mass) of the ink composition, 10 to40% by mass of a vinyl ether group-containing (meth)acrylate representedby the following general formula (I):

CH₂═CR¹—COOR²—O—CH═CH—R³  (I)

(wherein R¹ is a hydrogen atom or a methyl group, R² is a divalentorganic residue having 2 to 20 carbon atoms, and R³ is a hydrogen atomor a monovalent organic residue having 1 to 11 carbon atoms), 20 to 60%by mass of a monofunctional (meth)acrylate (excluding the vinyl ethergroup-containing (meth)acrylate represented by the general formula (I)),and 10 to 40% by mass of a polyfunctional (meth)acrylate.

Hereinafter, additives (components) which are contained or can becontained in the ink composition according to the embodiment aredescribed.

[Polymerizable Compound]

The polymerizable compounds contained in the ink composition accordingto the embodiment are capable of curing an printed ink by polymerizationcaused by the action of the photopolymerization initiator describedbelow during ultraviolet irradiation.

(Vinyl Ether Group-Containing (Meth)Acrylate)

The vinyl ether group-containing (meth)acrylate contained as anessential polymerizable compound in the embodiment is represented by thegeneral formula (I).

When the ink composition contains the vinyl ether group-containing(meth)acrylate, curability of an ink can be improved, and the viscosityof an ink can be further decreased. Furthermore, when a compoundcontaining both a vinyl ether group and a (meth)acryl group in itsmolecule is used, ink curability is desirably more improved as comparedwith when a vinyl ether group-containing compound and a (meth)acrylgroup-containing compound are separately used.

In the general formula (I), a divalent organic residue represented by R²and having 2 to 20 carbon atoms is preferably a linear, branched, orcyclic alkylene group which has 2 to 20 carbon atoms and may besubstituted, an alkylene group which has 2 to 20 carbon atoms, containsan oxygen atom through an ether bond and/or an ester bond in itsstructure, and which may be substituted, or a divalent aromatic groupwhich has 6 to 11 carbon atoms and may be substituted. Preferredspecific examples of these groups include alkylene groups having 2 to 6carbon atoms, such as an ethylene group, a n-propylene group, anisopropylene group, a butylene group, and the like; and alkylene groupshaving 2 to 9 carbon atoms and an oxygen atom through an ether bond inits structure, such as an oxyethylene group, an oxy-n-propylene group,an oxyisopropylene group, and an oxybutylene group, and the like.

In the general formula (I), a monovalent organic residue represented byR³ and having 1 to 11 carbon atoms is preferably a linear, branched, orcyclic alkyl group which has 1 to 10 carbon atoms and may besubstituted, or an aromatic group which has 6 to 11 carbon atoms and maybe substituted. Preferred examples of these groups include alkyl groupshaving 1 to 2 carbon atoms, such as a methyl group and an ethyl group,and aromatic groups having 6 to 8 carbon atoms, such as a phenyl groupand a benzyl group.

When each of the organic residues is a group which may be substituted,substituents are divided into groups containing a carbon atom and groupsnot containing a carbon atom. When a substituent is a group containing acarbon atom, the carbon atom is counted in the number of carbon atoms ofthe organic residue. Examples of the group containing a carbon atominclude, but are not limited to, a carboxyl group and an alkoxy group.Examples of the group not containing a carbon atom include, but are notlimited to, a hydroxyl group and a halo-group.

Examples of the vinyl ether group-containing (meth)acrylate include, butare not limited to, 2-vinyloxyethyl (meth)acrylate, 3-vinyloxypropyl(meth)acrylate, 1-methyl-2-vinyloxyethyl (meth)acrylate,2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl (meth)acrylate,1-methyl-3-vinyloxypropyl (meth)acrylate, 1-vinyloxymethylpropyl(meth)acrylate, 2-methyl-3-vinyloxypropyl (meth)acrylate,1,1-dimethyl-2-vinyloxyethyl (meth)acrylate, 3-vinyloxybutyl(meth)acrylate, 1-methyl-2-vinyloxypropyl (meth)acrylate,2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl (meth)acrylate,6-vinyloxyhexyl (meth)acrylate, 9-vinyloxymethylcyclohexylmethyl(meth)acrylate, 3-vinyloxymethylcyclohexylmethyl (meth)acrylate,2-vinyloxymethylcyclohexylmethyl (meth)acrylate,p-vinyloxymethylphenylmethyl (meth)acrylate,m-vinyloxymethylphenylmethyl (meth)acrylate,o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl(meth)acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyethoxy) propyl (meth)acrylate, 2-(vinyloxyethoxy) isopropyl(meth)acrylate, 2-(vinyloxyisopropoxy) propyl (meth)acrylate,2-(vinyloxyisopropoxy) isopropyl (meth)acrylate,2-(vinyloxyethoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyethoxy)propyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy) propyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyethoxyethoxy) isopropyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)isopropyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,polyethylene glycol monovinyl ether (meth)acrylate, and polypropyleneglycol monovinyl ether (meth)acrylate.

Among these, 2-(vinyloxyethoxy)ethyl (meth)acrylate, i.e., at least oneof 2-(vinyloxyethoxy)ethyl acrylate and 2-(vinyloxyethoxy)ethylmethacrylate, is preferred, and 2-(vinyloxyethoxy)ethyl acrylate is morepreferred because the ink can be decreased in viscosity and has a highflashing point and more excellent curability. In particular, any one of2-(vinyloxyethoxy)ethyl acrylate and 2-(vinyloxyethoxy)ethylmethacrylate has a simple structure and a low molecular weight, and thusthe viscosity of the ink can be further decreased. Examples of2-(vinyloxyethoxy)ethyl (meth)acrylate include 2-(2-vinyloxyethoxy)ethyl(meth)acrylate and 2-(1-vinyloxyethoxy)ethyl (meth)acrylate. Examples of2-(vinyloxyethoxy)ethyl acrylate include 2-(2-vinyloxyethoxy)ethylacrylate and 2-(1-vinyloxyethoxy)ethyl acrylate. In addition,2-(vinyloxyethoxy)ethyl acrylate is superior in curability to2-(vinyloxyethoxy)ethyl methacrylate.

These vinyl ether group-containing (meth)acrylates may be used alone orin combination of tow or more.

The content of the vinyl ether group-containing (meth)acrylate is 10 to40% by mass relative to the total mass (100% by mass) of the inkcomposition. When the content is 10% by mass or more, the curability ofthe ink is particularly excellent. On the other hand, when the contentis 40% by mass or less, particularly, the occurrence of curing wrinklescan be prevented. In order to achieve more excellent curability of theink and more effectively prevent the occurrence of curing wrinkles, thecontent is preferably 10 to 35% by mass, more preferably 10 to 30% bymass, still more preferably 20 to 30% by mass, relative to the totalmass (100% by mass) of the ink composition.

Examples of a method for producing the vinyl ether group-containing(meth)acrylate include, but are not limited to, a method (method B) ofesterifying (meth)acrylic acid with hydroxyl group-containing vinylether, a method (method C) of esterifying (meth)acrylic acid halide withhydroxyl group-containing vinyl ether, a method (method D) ofesterifying (meth)acrylic anhydride with hydroxyl group-containing vinylether, a method (method E) of ester-exchanging (meth)acrylate withhydroxyl group-containing vinyl ether, a method (method F) ofesterifying (meth)acrylic acid with halogen-containing vinyl ether, amethod (method G) of esterifying (meth)acrylic acid alkali (earth) metalsalt with halogen-containing vinyl ether, a method (method H) ofvinyl-exchanging hydroxyl group-containing (meth)acrylate with vinylcarboxylate, and a method (method I) of ether-exchanging hydroxylgroup-containing (meth)acrylate with alkyl vinyl ether.

Among these, the method E is preferred because a desired effect can bemore exhibited in the embodiment.

(Monofunctional (Meth)Acrylate)

The ink composition according to the embodiment contains themonofunctional (meth)acrylate. Since the ink composition contains themonofunctional (meth)acrylate, particularly, particularly, theextensibility of a cured film can be improved. However, the vinyl ethergroup-containing (meth)acrylate represented by the general formula (I)is excluded from the monofunctional (meth)acrylate.

Examples thereof include, but are not limited to, isoamyl(meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl(meth)acrylate, decyl (meth)acrylate, isomyristyl (meth)acrylate,isostearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate,2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate,butoxyethyl (meth)acrylate, ethoxy diethylene glycol (meth)acrylate,methoxy diethylene glycol (meth)acrylate, methoxy polyethylene glycol(meth)acrylate, methoxy propylene glycol (meth)acrylate, phenoxyethyl(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate,lactone-modified flexible (meth)acrylate, tert-butylcyclohexyl(meth)acrylate, dicyclopentanyl (meth)acrylate, anddicyclopentenyloxyethyl (meth)acrylate.

Among these, phenoxyethyl (meth)acrylate is preferred, and phenoxyethylacrylate is more preferred because compatibility with the additives suchas the photopolymerization initiator can be improved, viscosity and odorcan be decreased, and the curability of the ink can be further improved.

The primary skin irritation index (P. I. I.) of the monofunctional(meth)acrylate is preferably 0 to 4 and more preferably 0 to 3 becauseskin irritation can be suppressed, and ink safety can be improved.

These monofunctional (meth)acrylates may be used alone or in combinationof two or more.

The content of the monofunctional (meth)acrylate is 20 to 60% by massrelative to the total mass (100% by mass) of the ink composition. Whenthe content is 20% by mass or more, the extensibility of a cured film isexcellent. On the other hand, when the content is 60% by mass or less,the occurrence of curing wrinkles can be prevented. In order to achievemore excellent extensibility of a cured film and more effectivelyprevent the occurrence of curing wrinkles, the content is preferably 25to 55% by mass, and more preferably 30 to 50% by mass. In addition,particularly, in order to prevent the occurrence of curing wrinkles, thecontent is preferably 40% by mass or less and more preferably 20 to 40%by mass.

The content of phenoxyethyl (meth)acrylate among the monofunctional(meth)acrylates is preferably 10 to 60% by mass and more preferably 10to 40% by mass relative to the total mass (100% by mass) of the inkcomposition. With a content within this range, the curability of the inkcan be further improved. In addition, when an acylphosphine oxidecompound is used as the photopolymerization initiator, the solubilitythereof can be improved.

(Polyfunctional (Meth)Acrylate)

The ink composition according to the embodiment contains thepolyfunctional (meth)acrylate. Since the ink composition contains thepolyfunctional (meth)acrylate, particularly, the occurrence of curingwrinkles can be prevented. In the specification, the polyfunctional(meth)acrylate represents bi- or higher-functional (meth)acrylate.

Examples of the bifunctional (meth)acrylate as the polyfunctional(meth)acrylate include, but are not limited to, triethylene glycoldi(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethyleneglycol di(meth)acrylate, dipropylene glycol di(meth)acrylate,tripropylene glycol di(meth)acrylate, polypropylene glycoldi(meth)acrylate, 1,4-dutanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, dimethyloltricyclodecane di(meth)acrylate, bisphenol AEO (ethylene oxide) adduct di(meth)acrylate, bisphenol A PO (propyleneoxide) adduct di(meth)acrylate, neopentyl glycol hydroxypivalatedi(meth)acrylate, and polytetramethylene glycol di(meth)acrylate. Amongthese, at least one selected from the group consisting of dipropyleneglycol diacrylate, tripropylene glycol diacrylate, anddimethyloltricyclodecane diacrylate is preferred because of excellentsafety and low skin irritation.

Examples of the tri- or higher-functional (meth)acrylate as thepolyfunctional (meth)acrylate include, but are not limited to,trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropanetri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate,ditrimethylolpropane tetra(meth)acrylate, glyceryl propoxytri(meth)acrylate, caprolactone-modified trimethylolpropanetri(meth)acrylate, pentaerythritolethoxy tetra(meth)acrylate, andcaprolactam-modified dipentaerythritol hexa(meth)acrylate. Among these,dipentaerythritol hexaacrylate is preferred because of excellent safetyand low skin irritation.

Besides the above, oligomers such as epoxy (meth)acrylate, urethane(meth)acrylates such as aliphatic urethane (meth)acrylate and aromaticurethane (meth)acrylate, polyester (meth)acrylate, and the like may beused as the polyfunctional (meth)acrylate. Among these, urethaneacrylate oligomers are preferred because of excellent flexibility.

These polyfunctional (meth)acrylates may be used alone or in combinationof two or more.

The content of the polyfunctional (meth)acrylate is 10 to 40% by massrelative to the total mass (100% by mass) of the ink composition. Whenthe content is 10% by mass or more, the occurrence of curing wrinklescan be prevented. On the other hand, when the content is 40% by mass orless, the extensibility of a cured film is excellent. In order to moreeffectively prevent the occurrence of curing wrinkles and achieve moreexcellent extensibility of a cured film, the content is preferably 15 to35% by mass and more preferably 20 to 30% by mass.

(Polymerizable Compound Other than the Above)

Besides the vinyl ether group-containing (meth)acrylate, themonofunctional (meth)acrylate, and the polyfunctional (meth)acrylate,any one of various known monofunctional and polyfunctional monomers andoligomers can be further used (hereinafter, referred to as the “otherpolymerizable compound”). Examples of the monomers include unsaturatedcarboxylic acids such as itaconic acid, crotonic acid, isocrotonic acid,maleic acid, and the like, salts or esters thereof, urethane, amides andanhydrides thereof, acrylonitrile, styrene, various unsaturatedpolyesters, unsaturated polyethers, unsaturated polyamides, andunsaturated urethane. Examples of the oligomers include oligomers formedfrom the monomers.

These other polymerizable compounds may be used alone or in combinationof two or more. The content of the other polymerizable compound ispreferably 50% by mass or less relative to the total mass (100% by mass)of the ink composition.

[Photopolymerization Initiator]

The photopolymerization initiator contained in the ink compositionaccording to the embodiment is used for curing an ink present on asurface of a recording medium by photopolymerization under ultravioletirradiation to form a print. Among radiations, the use of ultravioletlight (UV) exhibits excellent safety and can suppress the cost of alight source lamp. The photopolymerization initiator is not limited aslong as active species such as radical or cation are produced by light(ultraviolet light) energy to initiate polymerization of thepolymerizable compounds. However, a photo-radical polymerizationinitiator and a photo-cationic polymerization initiator can be used, andparticularly, the photo-radical polymerization initiator is preferablyused.

Examples of the photo-radical polymerization initiator include aromaticketones, acylphosphine oxide compounds, aromatic onium salt compounds,organic peroxides, thio compounds (thioxanthone compounds, thiophenylgroup-containing compounds, and the like), hexaaryl biimidazolecompounds, ketoxime ester compounds, borate compounds, aziniumcompounds, metallocene compounds, active ester compounds, compoundshaving carbon-halogen bonds, and alkylamine compounds.

Among these, the acylphosphine oxide compounds are more preferably used,and the acylphosphine oxide compounds are still more preferably used incombination with the thioxanthone compounds particularly because thecurability of an ink can be further improved.

Specific examples of the photo-radical polymerization initiator includeacetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenylketone, 2,2-dimethoxy-2-phenyl acetophenone, xanthone, fluorenone,benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole,3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone,4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether,benzoin ethyl ether, benzyl dimethyl ketal,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one,2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone,diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide,2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide,2,4-diethylthioxanthone, andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide.

Examples of commercial products of the photo-radical polymerizationinitiator include IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethan-1-one),IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173(2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959(1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one),IRGACURE 127(2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl]-2-methyl-propan-1-one},IRGACURE 907 (2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one),IRGACURE 369(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1), IRGACURE379(2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone),DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), IRGACURE 784(bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium),IRGACURE OXE 01 (1.2-octanedione, 1-[4-(phenylthio)-,2-(O-benzoyloxime)]), IRGACURE OXE 02 (ethanone,1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime)),and IRGACURE 754 (mixture of oxyphenylacetic acid,2-[2-oxo-2-phenylacetoxyethoxy]ethyl ester and oxyphenylacetic acid, and2-(2-hydroxyethoxy)ethyl ester) (manufactured by BASF Corporation),KAYACURE DETX-S (2,4-diethylthioxanthone) (trade name, manufactured byNippon Kayaku Co., Ltd.), Lucirin TPO, LR8893, and LR8970 (manufacturedby BASF Corporation), and UBECRYL P36 (manufactured by UCB Corporation).

These photopolymerization initiators may be used alone or in combinationof two or more.

The content of the photopolymerization initiator is preferably 5 to 20%by mass and more preferably 5 to 15% by mass relative to the total mass(100% by mass) of the ink composition in order to achieve the excellentcurability by improving the ultraviolet curing rate and avoid coloringdue to the photopolymerization initiator and avoid thephotopolymerization initiator from remaining undissolved.

In particular, when the photopolymerization initiator contains anacylphosphine oxide compound, the content of the acylphosphine oxidecompound is preferably 6 to 13% by mass and more preferably 7 to 12% bymass relative to the total mass (100% by mass) of the ink composition.This is because a satisfactory curing rate can be achieved by curingwith LED (preferably, emission peak wavelength: 350 nm to 420 nm),thereby exhibiting more excellent curability.

[Colorant]

The ink composition according to the embodiment may further contain acolorant. As the colorant, at least one of a pigment and a dye can beused.

(Pigment)

In the embodiment, the light resistance of the ink composition can beimproved by using a pigment as the colorant. As the pigment, either aninorganic pigment or an organic pigment can be used.

Usable examples of the inorganic pigment include carbon black (C. I.Pigment Black 7) such as furnace black, lamp black, acetylene black,channel black, and the like, iron oxide, and titanium oxide.

Usable examples of the organic pigment include azo pigments such asinsoluble azo pigments, condensed azo pigments, azo-lakes, chelate azopigments, and the like; polycyclic pigments such as phthalocyaninepigments, perylene and perynone pigments, anthraquinone pigments,quinacridone pigments, dioxane pigments, thioindigo pigments,isoindolinone pigments, quinophthalone pigments, and the like; dyechelates (e.g., basic dye-type chelates, acid dye-type chelates, and thelike), dye lakes (basic dye-type lakes and acid dye-type lakes), nitropigments, nitroso pigments, aniline black, and daylight fluorescentpigments.

In further detail, examples of carbon black used as a black ink includeNo. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8,MA100, No. 2200B, and the like (trade names, manufactured by MitsubishiChemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500,Raven 1255, Raven 700, and the like (trade names, manufactured by CarbonColumbia Corporation), Regal 400R, Regal 330R, Regal 660R, Mogul L,Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000,Monarch 1100, Monarch 1300, Monarch 1400, and the like (trade names,manufactured by CABOT JAPAN K.K.), and Color Black FW1, Color Black FW2,Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150,Color Black S160, Color Black S170, Printex 35, Printex U, Printex V,Printex 140U, Special Black 6, Special Black 5, Special Black 4A,Special Black 4, and the like (trade names, manufactured by DegussaCorporation).

Examples of a pigment used as a white ink include C. I. Pigment White 6,18, and 21.

Examples of a pigment used as a yellow ink include C. I. Pigment Yellow1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55,65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114,117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172,and 180.

Examples of a pigment used as a magenta ink include C. I. Pigment Red 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23,30, 31, 32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 88,112, 114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176,177, 178, 179, 184, 185, 187, 202, 209, 219, 224, and 245, and C. I.Pigment Violet 19, 23, 32, 33, 36, 38, 43, and 50.

Examples of a pigment used as a cyan ink include C. I. Pigment Blue 1,2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, and 66,and C. I. Vat Blue 4 and 60.

Examples of pigments other than magenta, cyan, yellow include C. I.Pigment Green 7 and 10, C. I. Pigment Brown 3, 5, 25, and 26, C. I.Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, and63.

These pigments may be used alone or in combination of two or more.

(Dye)

In the embodiment, a dye can be used as the colorant. The dye is notparticularly limited, and an acid dye, a direct dye, a reactive dye, anda basic dye can be used. Examples of the dye include C. I. Acid Yellow17, 23, 42, 44, 79, and 142, C. I. Acid Red 52, 80, 82, 249, 254, and289, C. I. Acid Blue 9, 45, and 249, C. I. Acid Black 1, 2, 24, and 94,C. I. Food Black 1 and 2, C. I. Direct Yellow 1, 12, 24, 33, 50, 55, 58,86, 132, 142, 144, and 173, C. I. Direct Red 1, 4, 9, 80, 81, 225, and227, C. I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, and 202, C.I. Direct Black 19, 38, 51, 71, 154, 168, 171, and 195, C. I. ReactiveRed 14, 32, 55, 79, and 249, and C. I. Reactive Black 3, 4, and 35.

These dyes may be used alone or in combination of two or more.

The content of the colorant is preferably 1 to 20% by mass relative tothe total mass (100% by mass) of the ink composition because goodcoloring properties can be exhibited, and the inhibition of curing of acoating film due to light absorption by the colorant can be decreased.An ink composition containing a colorant is generally inferior to an inkcomposition not containing a colorant in curability and, particularly,internal curability of a thick film when thick-film recording isperformed. However, the photocurable ink composition according to theembodiment can produce a good recorded material by using a predeterminedconfiguration even when containing a colorant.

[Dispersant]

When the ink composition according to the embodiment contains a pigment,the ink composition may further contain a dispersant for improvingpigment dispersibility. Examples of the dispersant include, but are notlimited to, dispersants such as polymeric dispersants commonly used forpreparing pigment dispersion solutions. Specific examples thereofinclude those each containing, as a main component, at least one ofpolyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers,acryl polymers and copolymers, polyesters, polyamides, polyimides,polyurethanes, amino polymers, silicon-containing polymers,sulfur-containing polymers, fluorine-containing polymers, and epoxyresins. Commercial products of the polymeric dispersants include AjisperSeries (trade name) manufactured by Ajinomoto Fine-Techno Co., Inc.,Solsperse Series (Solsperse 32000, 36000, etc. (trade name)) availablefrom Avecia Co., Disperbyk Series (trade name) manufactured by BYKChemie Co., Ltd. and Disparlon Series (trade name) manufactured byKusumoto Chemical Ltd.

These dispersants may be used alone or in combination of two or more.The content of the dispersant is not particularly limited, and thedispersant may be added in an appropriate desired amount.

[Other Additives]

The ink composition according to the embodiment may further containadditives (components) other than the above-described additives. Thesecomponents are not particularly limited, but, for example, a generallyknown polymerization accelerator, polymerization inhibitor, slippingagent (surfactant), permeation accelerator, and wetting agent(humectant), and other additives can be used. Examples of the otheradditives include a generally known fixing agent, fungicide, antiseptic,antioxidant, ultraviolet absorber, chelating agent, pH adjuster, andthickener.

In addition, the ink composition can be cured by irradiation withultraviolet light preferably having an emission peak wavelength withinthe range of 350 to 420 nm, more preferably 360 to 400 nm. When the inkcomposition of the embodiment can be cured at an emission peakwavelength within the above-described range, the ink composition can berapidly cured with low energy due to the composition. In particular, thepossibility of curing with low energy preferably leads to thepossibility of using a light-emitting diode (LED), which has recentlyattracted attention from the environmental viewpoint, as an ultravioletirradiation source. That is, the ink composition of the embodiment ofthe present invention is excellent in curability with LED.

In addition, the ink composition is preferably cured with an ultravioletirradiation energy of 300 mJ/cm² or less, more preferably 200 mJ/cm² orless. By using the ink composition, an image can be formed at low cost.The irradiation energy is calculated by multiplying the irradiation timeby the irradiation intensity.

According to the embodiment, it is possible to provide the photocurableink composition for ink jet recording which has excellent curability andexcellent extensibility of a cured film, and which is capable ofpreventing the occurrence of curing wrinkles when a thick film is cured.

[Recording Medium]

The ink composition according to the embodiment of the present inventionis ejected on a recording medium by an ink jet recording methoddescribed below to form a recorded material. As the recording medium,for example, an absorbent or non-absorbent recording medium can be used.The ink jet recording method according to an embodiment described belowcan be widely applied to recording media having various absorptionperformances, ranging from a non-absorbent recording medium which anaqueous ink hardly permeates to an absorbent recording medium which anaqueous ink easily permeates. However, when the ink composition isapplied to the non-absorbent recording medium, a drying step may berequired after curing by ultraviolet irradiation.

Examples of the absorbent recording medium include, but are not limitedto, plain paper such as electrophotographic paper with high permeabilityto aqueous ink, ink jet paper (ink jet exclusive paper provided with anink-absorbing layer composed of silica particles or alumina particles oran ink-absorbing layer composed of a hydrophilic polymer such aspolyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), or the like), andart paper, coated paper, cast paper, and the like which have relativelylow permeability to aqueous ink and which are used for general offsetprinting.

Examples of the non-absorbent recording medium include, but are notlimited to, plastic films, sheets, and plates of polyvinyl chloride(PVC), polyethylene, polypropylene, polyethylene terephthalate (PET),and the like; metal plates of iron, silver, copper, aluminum, and thelike; metal plates and plastic films produced by vapor-depositing anyone of the metals; alloy plates of stainless, brass, and the like.

[Ink Jet Recording Method]

An embodiment of the present invention relates to an ink jet recordingmethod. The photocurable ink composition for ink jet recording accordingto the above-described embodiment of the present invention can be usedin the ink jet recording method according to this embodiment. The inkjet recording method of the embodiment includes an ejection step ofejecting the ink composition on a recording medium, and a curing step ofcuring the ink composition by ultraviolet irradiation of the inkcomposition ejected in the ejection step. Therefore, an image, i.e., acoating film (cured film), is formed of the ink composition cured on therecording medium.

[Ejection Step]

In the ejection step, the ink composition is ejected on the recordingmedium and adheres to the recording medium. The viscosity of the inkcomposition during ejection is preferably 5 to 30 mPa·s. When theviscosity of the ink composition is the above-described value under acondition where the ink composition is at room temperature or is notheated, the ink composition may be ejected at room temperature orwithout heating. In this case, the ink temperature during ejection ispreferably 20 to 30° C. On the other hand, the ink composition may beejected with desired viscosity by heating to a predeterminedtemperature. In this way, good ejection stability can be realized.

The photocurable ink composition for ink jet recording of the embodimentof the present invention has higher viscosity than that of a usualaqueous ink composition and thus causes a large change in viscosity witha temperature change during ejection. Such a change in viscosity of theink greatly influences a change in droplet size and a change in dropletejection rate, resulting in the occurrence of deterioration in imagequality. Therefore, the temperature of ink during ejection is preferablymaintained as constant as possible.

[Curing Step]

In the next curing step, the ink composition ejected and adhering to therecording medium is cured by light (ultraviolet light) irradiation. Thisis due to that the photopolymerization initiator contained in the inkcomposition is decomposed by ultraviolet irradiation to produceinitiation species such as radical, acid, and base, thereby acceleratingpolymerization reaction of the polymerizable compounds by the functionof the initiation species. Alternatively, the polymerization reaction ofthe polymerizable compounds is initiated by ultraviolet irradiation. Inthis case, when a sensitizing dye is present together with thephotopolymerization initiator in the ink composition, the sensitizingdye in the system comes into an excited state by absorbing ultravioletlight and accelerates decomposition of the photopolymerization initiatorby contact with the photopolymerization initiator, so thathigh-sensitivity curing reaction can be achieved.

A mercury lamp, a gas/solid-state laser, and the like are mainly used asultraviolet sources, and a mercury lamp and a metal halide lamp arewidely known as light sources used for curing photocurable inkcompositions for ink jet recording. On the other hand, at present, amercury-free type is strongly demanded from the viewpoint ofenvironmental protection, and the replacement by a GaN-basedsemiconductor ultraviolet light-emitting device is very useful from theindustrial and environmental viewpoint. Further, an ultravioletlight-emitting diode (UV-LED) and an ultraviolet laser diode (UV-LD)have a small size, long life, high efficiency, and low cost, and arethus expected as a light source for photocurable ink jet. In particular,UV-LED is preferred.

In addition, the photocurable ink composition for ink jet recordingwhich can be cured preferably with an irradiation energy of 300 mJ/cm²or less may be preferably used in the ink jet recording method using aUV-LED having an emission peak wavelength within the range of 350 to 420nm because the output of LED can be easily increased. In this case,low-cost printing and a high printing speed can be realized. Such an inkcomposition can be produced by containing at least one of thephotopolymerization initiator which is decomposed by irradiation withultraviolet light within the above-described wavelength range and thepolymerizable compound which is initiated to be polymerized byirradiation with ultraviolet light within the above-described wavelengthrange.

According to the embodiment, it is possible to provide the low-cost inkjet recording method having a high printing speed and contributing toenvironmental protection by using the photocurable ink composition forink jet recording which has excellent curability and excellentextensibility of a cured film and which is capable of preventing theoccurrence of curing wrinkles when a thick film is cured.

EXAMPLES

The first embodiment of the present invention is described in furtherdetail below with reference to examples, but the embodiment is notlimited to these examples.

[Components Used]

The components used in examples and comparative examples described beloware as follows.

[Pigment]

-   -   IRGALITE BLUE GLVO (cyan pigment (C. I. Pigment Blue 15:4),        trade name, manufactured by BASF Corporation, abbreviated as        “BLUE GLVO” hereinafter)

[Dispersant]

-   -   Solsperse 32000 (trade name, manufactured by LUBRIZOL        Corporation, abbreviated as “SOL32000” hereinafter)

[Vinyl Ether Group-Containing (Meth)Acrylate]

-   -   VEEA (2-(2-vinyloxyethoxy)ethyl acrylate, trade name,        manufactured by Nippon Shokubai Co., Ltd., abbreviated as “VEEA”        hereinafter). In tables below, the vinyl ether group-containing        (meth)acrylate is shown as “Acryl vinyl-containing monomer”.

[Monofunctional (Meth)Acrylate]

-   -   Viscoat #192 (phenoxyethyl acrylate, trade name, manufactured by        OSAKA ORGANIC CHEMICAL INDUSTRY LTD., abbreviated as “PEA”        hereinafter)    -   IBXA (isobornyl acrylate, trade name, manufactured by OSAKA        ORGANIC CHEMICAL INDUSTRY LTD., abbreviated as “IBXA”        hereinafter)

[Polyfunctional (Meth)Acrylate]

-   -   NK Ester APG-100 (dipropylene glycol diacrylate, trade name,        manufactured by SHIN-NAKAMURA CHEMICAL CO., LTD., abbreviated as        “DPGDA” hereinafter)    -   NK Ester APG-200 (tripropylene glycol diacrylate, trade name,        manufactured by SHIN-NAKAMURA CHEMICAL CO., LTD., abbreviated as        “TPGDA” hereinafter)

[Photopolymerization Initiator]

-   -   IRGACURE 819 (trade name, manufactured by BASF Corporation,        solid content 100%, abbreviated as “819” hereinafter)    -   Speedcure TPO (trade name, manufactured by Lambson Ltd., solid        content 100%, abbreviated as “TPO” hereinafter)    -   Speedcure DETX (trade name, manufactured by Lambson Ltd., solid        content 100%, abbreviated as “DETX” hereinafter)

[Polymerization Inhibitor]

-   -   p-Methoxyphenol (trade name, manufactured by Tokyo Chemical        Industry Co., Ltd., p-methoxyphenol, abbreviated as “MEHQ”        hereinafter)

[Slipping Agent]

-   -   BYK-UV3500 (trade name, manufactured by BYK Corporation,        abbreviated as “UV3500” hereinafter)

Examples 1 to 16 and Comparative Examples 1 to 6 [Preparation of PigmentDispersion Solution]

A pigment dispersion solution was prepared prior to preparation of anink composition. A pigment, a dispersant, and polymerizable compoundsdescribed in “Dispersion-derived monomer” of Tables 1 and 2 below weremixed to have each of the compositions (unit: % by mass) shown in Tables1 and 2 below, followed by stirring with a stirrer for 1 hour. Afterstirring, the resultant mixture was dispersed with a beads mill toprepare a pigment dispersion solution. Dispersion was performed withzirconia beads having a diameter of 0.65 mm and packed at a packing rateof 70% under the conditions including a peripheral speed of 9 m/s and adispersion time of 2 to 4 hours.

[Preparation of Ink Composition]

The components shown in Tables 1 and 2 below were added and mixed tohave each of the compositions (unit: % by mass) shown in Tables 1 and 2below (a pigment, a dispersant, and polymerizable compounds described in“Dispersion-derived monomer” of Tables 1 and 2 below were mixed as thepigment dispersion solution). The resultant mixture was stirred with ahigh-speed water-cooled stirrer to prepare a cyan-color photocurable inkcomposition for ink jet recording.

TABLE 1 Exam- Example 1 Example 2 Example 3 Example 4 Example 5 Example6 Example 7 Example 8 Example 9 ple 10 Pigment BLUE 2.0 2.0 2.0 2.0 2.02.0 2.0 2.0 2.0 2.0 GLVO Dispersant SOL32000 0.5 0.5 0.5 0.5 0.5 0.5 0.50.5 0.5 0.5 Dispersion-derived PEA 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.57.5 monomer IBXA Acryl vinyl ether- VEEA 20.0 10.0 30.0 20.0 20.0 28.010.0 10.0 30.0 20.0 containing monomer Monofunctional PEA 24.5 30.0 25.513.5 31.5 3.5 42.5 51.3 1.5 27.8 monomer IBXA Polyfunctional DPGDA 31.831.8 20.8 42.8 24.8 36.8 19.3 10.5 32.8 31.8 monomer TPGDA 4.5 8.0 4.54.5 12.0 Polymerization MEHQ 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2inhibitor Slipping agent UV3500 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2Photopolymerization 819 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 4.0initiator TPO 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 3.5 DETX 2.5 2.5 2.52.5 2.5 2.5 2.5 2.5 2.5 2.5 Total 100.0 100.0 100.0 100.0 100.0 100.0100.0 100.0 100.0 100.0 PEA total 32.0 37.5 33.0 21.0 39.0 11.0 50.058.8 9.0 35.3 (819 + TPO) total 10.8 10.8 10.8 10.8 10.8 10.8 10.8 10.810.8 7.5

TABLE 2 Comp. Comp. Comp. Exam- Exam- Exam- Exam- Exam- Exam- Exam-Exam- Comp. Comp. Comp. ple 11 ple 12 ple 13 ple 14 ple 15 ple 1 ple 2ple 3 Example 4 Example 5 Example 6 Pigment BLUE GLVO 2.0 2.0 2.0 2.02.0 2.0 2.0 2.0 2.0 Dispersant SOL32000 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.50.5 Dispersion-derived PEA 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 monomer IBXA7.5 7.5 7.5 Acryl vinyl ether- VEEA 20.0 20.0 20.0 35.0 45.0 20.0 20.020.0 containing monomer Monofunctional PEA 27.8 27.8 27.8 30.0 10.0 10.031.3 31.3 monomer IBXA 11.3 10.0 26.3 28.8 Polyfunctional DPGDA 24.829.3 25.3 5.8 10.0 30.0 30.0 28.3 10.0 30.0 12.5 monomer TPGDA 5.5 26.328.0 35.0 35.0 Polymerization MEHQ 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.20.2 0.2 inhibitor Slipping agent UV3500 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.20.2 0.2 0.2 Photopolymerization 819 8.0 8.0 8.0 6.0 6.0 6.0 6.0 6.0 6.06.0 6.0 initiator TPO 6.5 2.0 6.0 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 DETX2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Total 100.0 100.0 100.0100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 PEA total 35.3 35.3 35.337.5 17.5 17.5 0.0 0.0 38.8 0.0 38.8 (819 + TPO) total 14.5 10.0 14.010.8 10.8 10.8 10.8 10.8 10.8 10.8 10.8

[Evaluation Item]

The photocurable ink composition for ink jet recording prepared in eachof the examples and the comparative examples was evaluated with respectto viscosity, solubility of the photopolymerization initiator,curability, adhesion, and abrasion resistance by methods describedbelow.

(1. Viscosity)

The viscosity of the ink composition of each of the examples and thecomparative examples was measured with a DVM-E-type rotary viscometer(manufactured by TOKYO KEIKI INC.) under the conditions of a temperatureof 25° C. and a rotational speed of 10 rpm. The evaluation criteria wereas described below. The evaluation results are shown in Tables 3 and 4below.

A: 25 mPa·s or less

B: over 25 mPa·s and less than 35 mPa·s

C: 35 mPa·s or more

(2. Solubility of Photopolymerization Initiator)

A pigment-free ink composition was prepared by the same method as in theabove-described examples and comparative examples except that thecomponents other than the pigment and the pigment dispersant were used.The resultant mixture was sufficiently stirred to prepare an inkcomposition. Then, whether or not the photopolymerization initiatorremained undissolved was visually observed. The ink composition withoutthe photopolymerization initiator remaining undissolved was placed in aconstant-temperature oven of 0° C., taken out 24 hours after, andreturned to room temperature. Then, whether or not thephotopolymerization initiator precipitated was again visually observed.

The evaluation criteria were as described below. The evaluation resultsare shown in Tables 3 and 4 below. In Tables 3 and 4, this evaluationitem is abbreviated as “Initiator solubility”.

A: Undissolved residue and precipitation of the photopolymerizationinitiator were not observed both after stirring at room temperature andafter storage at 0° C.

B: Undissolved residue of the photopolymerization initiator was notobserved after stirring at room temperature but precipitation of thephotopolymerization initiator was observed after storage at 0° C.

C: Undissolved residue of the photopolymerization initiator was observedafter stirring at room temperature

(3. Curability)

An ink jet recording apparatus provided with piezo-type ink jet nozzleswas used, and the nozzle array was filled with the ink composition ofeach of the examples and the comparative examples. A solid pattern image(recording resolution: 720×720 dpi) was printed on a PVC sheet(Flontlite Grossy 120g (trade name), manufactured by Cooley Co., Ltd.)at normal temperature and normal pressure while the amount of inkejected was controlled so that the thickness of a printed matter(recorded material) was 10 μm. In this case, each of the inkcompositions exhibited good ejection properties. In addition, the solidpattern image was cured by increasing the number of paths until theimage became tack-free using UV-LED in an ultraviolet irradiationapparatus provided at the side of a carriage under irradiationconditions of an irradiation intensity of 1 W/cm², and an ultravioletpeak wavelength of 395 nm, an irradiation energy of 100 mJ/cm² per path.As a result, a recorded material having the solid pattern image printedon the PVC sheet was formed.

The “solid pattern image” is an image in which dots are recorded in allpixels in a minimum recording unit region defined by the recordingresolution. The “number of paths” represents the number of times ofultraviolet irradiation performed on a coating film by moving a headprovided with the ultraviolet irradiation apparatus toward the recordedmaterial. The irradiation energy (mJ/cm²) was determined by measuringthe irradiation intensity (mW/cm²) on a surface irradiated from thelight source and multiplying the irradiation intensity by theirradiation duration time (s). The irradiation intensity was measuredusing an ultraviolet ray intensity meter UM-10 and a light receivingunit UM-400 (both manufactured by KONICA MINOLTA SENSING, INC.).

The curability of a coating film was evaluated using as an index theirradiation energy when it was tack-free. Whether or not a coating filmbecame tack-free was determined under conditions described below. Thatis, it was determined whether or not an ink adhered to a cotton-tippedswab or whether or not an ink cured product on a recording medium wasscratched. When the ink did not adhere to the cotton-tipped swab and theink cured product on the recording medium was not scratched, the coatingfilm was determined as being “tack-free”. In this case, thecotton-tipped swab used was a Johnson cotton-tipped swab manufactured byJohnson & Johnson Co. Ltd. The number of rubbing cycles was 10, and therubbing strength was a 100-g load.

The evaluation criteria were as described below. The evaluation resultsare shown in Tables 3 and 4 below.

A: 200 mJ/cm² or less

B: Over 200 mJ/cm² and 300 mJ/cm² or less

C: Over 300 mJ/cm²

(4. Adhesion)

The recorded material formed by ultraviolet irradiation curing until itbecame tack-free in the test of “3. Curability” was used. According toJIS K-5600-5-6 (ISO2409) (General Testing Methods for paints-Part 5:Mechanical properties of films-Section 6: Adhesion (cross-cut method)),a coating film surface of the recorded material was cross-cut andsubjected to a peel test using a cellophane tape. On the basis of theresults of the peel test, adhesion was evaluated according to ranks A toE below. The cross-cut method is described below.

A single-edge cutting tool (general commercial cutter) serving as acutting tool and a guide for cutting at equal intervals using thesingle-edge cutting tool were prepared.

First, the cutting tool was applied perpendicularly to a coating film tomake 6 cuts in the recorded material. After the 6 cuts were made, thedirection of the cutting tool was changed by 90°, and 6 cuts werefurther made to be perpendicular to the previously made cuts.

Next, a transparent adhesive tape (width 25±1 mm) was drawn to a lengthof about 75 mm, attached to a cross-cut portion formed on the coatingfilm, and sufficiently rubbed with a finger so that the coating filmcould be seen through the tape. Then, within 5 minutes afterapplication, the tape was securely peeled at an angle close to 60° over0.5 to 1.0 second.

The evaluation criteria were as described below. A value of each rankwas determined by rounding off a calculated peeling rate to the nearestnumber. The evaluation results are shown in Tables 3 and 4 below.

A: Peeling rate of 0 to 5%

B: Peeling rate of 6 to 15%

C: Peeling rate of 16 to 35%

D: Peeling rate of 36 to 65%

E: Peeling rate of 66 to 100%

(5. Abrasion Resistance)

According to JIS K5701 (ISO 11628) (definition of testing methods forlithographic inks, colored samples, and prints), abrasion resistance wasevaluated using a Gakushin-type rubbing fastness tester (manufactured byTESTER SANGYO CO., LTD.). An evaluation method included placing canequimon a surface of the recorded material produced in the test of “3.Curability”, rubbing with a load of 500 g, and visually observingpeeling on the cured surface of the recorded material after rubbing.

The evaluation criteria are as follows. The evaluation results are shownin Tables 3 and 4 below.

A: No stain was observed on canequim, and neither peel nor scratch wasobserved on the recorded surface.

B: Stain was observed on canequim, but neither peel nor scratch wasobserved on the recorded surface.

C: Stain was observed on canequim, and peel and linear scratch wereslightly observed on the recorded surface.

A: Stain was observed on canequim, and peel and scratch wassignificantly observed on the recorded surface.

TABLE 3 Example Example 1 Example 2 Example 3 Example 4 Example 5Example 6 Example 7 Example 8 Example 9 10 Curability A B A A A A B B BB Viscosity A A A A A A A A A A Adhesion A A A A A A A B A A Abrasion AA A A A A A A A A resistance Initiator solubility A A A A A A A A B A

TABLE 4 Compar- Compar- Compar- Example Example Example Example ExampleComparative Comparative Comparative ative ative ative 11 12 13 14 15Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Curability AA A A A C C C C B B Viscosity A A A A A C A B C A C Adhesion A A A B B CC B D B C Abrasion A A A B B A A B C A B resistance Initiator B A A A AC C C A C A solubility

The above results indicate that the photocurable ink composition (eachof the examples) containing the polymerizable compounds including thevinyl ether group-containing (meth)acrylate represented by the generalformula (I) and the phenoxyethyl (meth)acrylate, and thephotopolymerization initiator has, as compared with the ink compositionfor which this is not true (each comparative example), excellentcurability, low viscosity, and excellent solubility of thephotopolymerization initiator, adhesion, and abrasion resistance. Inaddition, the ink compositions of Comparative Examples 5 and 6 are inkcompositions without containing the colorant and the dispersant ofComparative Examples 2 and 4, respectively, and have good curability andimproved adhesion and abrasion resistance as compared with ComparativeExamples 2 and 4, respectively, but cannot be used for recording imagesbecause of the absence of the colorant. Further, although not shown inthe tables, curability evaluation was performed under the sameconditions as in Example 1 except that the irradiation intensity ofUV-LED was 500 mW/cm², and the irradiation energy per path was adjustedto the same as in the example by extending the irradiation time perpath. As a result, curability was evaluated as “B”, and wrinkles wereobserved in a surface of the solid pattern.

The second embodiment of the present invention is described in furtherdetail below with reference to examples, but the embodiment is notlimited to these examples.

[Components Used]

The components used in examples and comparative examples below are asfollows.

[Vinyl Ether Group-Containing (Meth)Acrylate]

-   -   VEEA (2-(2-vinyloxyethoxy)ethyl acrylate, trade name,        manufactured by Nippon Shokubai Co., Ltd., abbreviated as “VEEA”        hereinafter).

[Monofunctional (Meth)Acrylate]

-   -   2-MTA (2-methoxyethyl acrylate, trade name, manufactured by        OSAKA ORGANIC CHEMICAL INDUSTRY LTD., abbreviated as “2MEA”        hereinafter)    -   3-MBA (3-methoxybutyl acrylate, trade name, manufactured by        OSAKA ORGANIC CHEMICAL INDUSTRY LTD., abbreviated as “3MBA”        hereinafter)    -   V#160 (benzyl acrylate, trade name, manufactured by Hitachi        Chemical Co., Ltd., abbreviated as “BZA” hereinafter)    -   FA-THFA (tetrahydrofurfuryl acrylate, trade name, manufactured        by Hitachi Chemical Co., Ltd., abbreviated as “THFA”        hereinafter)    -   SR395 (isodecyl acrylate, trade name, manufactured by Sartomer        Company, abbreviated as “IDA” hereinafter)    -   LA (lauryl acrylate, trade name, manufactured by OSAKA ORGANIC        CHEMICAL INDUSTRY LTD., abbreviated as “LA” hereinafter)    -   MEDOL10 ((2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate,        trade name, manufactured by OSAKA ORGANIC CHEMICAL INDUSTRY        LTD.)    -   V#150D (tetrahydrofurfuryl oligoacrylate, manufactured by OSAKA        ORGANIC CHEMICAL INDUSTRY LTD., abbreviated as “THFOA”        hereinafter)    -   IBXA (isobornyl acrylate, trade name, trade name, manufactured        by OSAKA ORGANIC CHEMICAL INDUSTRY LTD., abbreviated as “IBXA”        hereinafter)    -   4-HBA (4-hydroxybutyl acrylate, trade name, manufactured by        OSAKA ORGANIC CHEMICAL INDUSTRY LTD., abbreviated as “4HBA”        hereinafter)    -   ACMO (acryloylmorpholine, trade name, manufactured by Kohjin        Co., Ltd., abbreviated as “ACMO” hereinafter)    -   Viscoat #192 (phenoxyethyl acrylate, trade name, manufactured by        OSAKA ORGANIC CHEMICAL INDUSTRY LTD., abbreviated as “PEA”        hereinafter    -   Light acrylate P2H-A (phenoxydiethylene glycol acrylate, trade        name, manufactured by Kyoeisha Chemical Co., Ltd., abbreviated        as “PDEGA” hereinafter)    -   FA-513AS (dicyclopentanyl acrylate, trade name, manufactured by        Hitachi Chemical Co., Ltd., abbreviated as “DCPtaA” hereinafter)    -   FA-511AS (dicyclopentenyl acrylate, trade name, manufactured by        Hitachi Chemical Co., Ltd., abbreviated as “DCPteA” hereinafter)    -   FA-512AS (dicyclopentenyloxyethyl acrylate, trade name,        manufactured by Hitachi Chemical Co., Ltd., abbreviated as        “DCPteOEA” hereinafter)    -   DA-141 (2-hydroxy-3-phenoxypropyl acrylate, trade name,        manufactured by Nagasechemtex Corporation, abbreviated as “HPPA”        hereinafter)

[Other Monofunctional Polymerizable Compound]

-   -   NVF (N-vinylformamide, trade name, manufactured by Arakawa        Chemical Industries, Ltd., abbreviated as “NVF” hereinafter)    -   V-CAP (N-vinylcaprolactam, trade name, manufactured by ISP Japan        Ltd., abbreviated as “NVC” hereinafter) [Polyfunctional        (meth)acrylate]    -   NK Ester APG-100 (dipropylene glycol diacrylate, trade name,        manufactured by SHIN-NAKAMURA CHEMICAL CO., LTD., abbreviated as        “2PGA” hereinafter)    -   NK Ester APG-200 (tripropylene glycol diacrylate, trade name,        manufactured by SHIN-NAKAMURA CHEMICAL CO., LTD., abbreviated as        “3PGA” hereinafter)    -   R-684 (dimethyloltricyclodecane diacrylate, trade name,        manufactured by Nippon Kayaku Co., Ltd., abbreviated as        “DMTCDDA” hereinafter)    -   A-DPH (dipentaerythritol hexaacrylate, trade name, manufactured        by SHIN-NAKAMURA CHEMICAL CO., LTD., abbreviated as “DPHA”        hereinafter)    -   EBECRYL8402 (urethane acrylate oligomer, trade name,        manufactured by DAICEL-CYTEC Co, Ltd., abbreviated as “UA”        hereinafter)

[Other Polyfunctional Polymerizable Compound]

-   -   TDVE (triethylene glycol divinyl ether, trade name, manufactured        by Maruzen Petrochemical CO, LTD., abbreviated as “TEG-DVE”        hereinafter)

[Photopolymerization Initiator]

-   -   IRGACURE 819 (trade name, manufactured by BASF corporation,        solid content 100%, abbreviated as “819” hereinafter)    -   DAROCUR TPO (trade name, manufactured by BASF Corporation, solid        content 100%, abbreviated as “TPO” hereinafter)    -   KAYACURE DETX-S (trade name, manufactured by Nippon Kayaku Co.,        Ltd., solid content 100%, abbreviated as “DETX-S” hereinafter)

[Pigment]

-   -   MICROLITH-WA Black C-WA (color index name: C. I. Pigment Black        7, trade name, manufactured by BASF Corporation, abbreviated as        “Black” hereinafter)

[Dispersant]

-   -   Solsperse 36000 (trade name, manufactured by LUBRIZOL        Corporation, abbreviated as “SOL36000” hereinafter)

Examples 1 to 33, Comparative Examples 1 to 19, and Reference Example 1

The components shown in tables below were mixed to have each of thecompositions (unit: % by mass) shown in the tables, and the resultantmixture was stirred with a high-speed water-cooled stirrer to prepare ablack-color photocurable ink composition for ink jet recording. Allmonofunctional acrylates used in the examples had a P. I. I. of 0 to 9.In the tables, a blank without a numerical value indicates no addition.

TABLE 5 Exam- Component name Abbreviation Example 1 Example 2 Example 3Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 ple 10 Acrylvinyl- VEEA 10.00 10.00 10.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00containing monomer Monofunctional 2MEA 10.00 (meth)acrylate 3MBA 10.00BZA 10.00 THFA 5.00 5.00 10.00 IDA 10.00 4HBA 10.00 10.00 10.00 10.00PEA 30.00 30.00 30.00 30.00 30.00 30.00 30.00 30.00 30.00 30.00 DCPteA10.00 5.00 HPPA 5.00 5.00 5.00 5.00 Polyfunctional 2PGA 20.00 20.0010.00 5.00 15.00 10.00 10.00 10.00 10.00 10.00 (meth)acrylate 3PGA 5.0010.00 5.00 DMTCDDA 5.00 10.00 10.00 10.00 10.00 10.00 DPHA 5.00 5.005.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 Photo- 819 5.00 5.00 5.00 5.005.00 5.00 5.00 5.00 5.00 5.00 polymerization TPO 5.00 5.00 5.00 5.005.00 5.00 5.00 5.00 5.00 5.00 initiator DETX-S 2.00 2.00 2.00 2.00 2.002.00 2.00 2.00 2.00 2.00 Pigment Black 2.00 2.00 2.00 2.00 2.00 2.002.00 2.00 2.00 2.00 Dispersant SOL36000 1.00 1.00 1.00 1.00 1.00 1.001.00 1.00 1.00 1.00 Total 100.00 100.00 100.00 100.00 100.00 100.00100.00 100.00 100.00 100.00

TABLE 6 Example Example Example Example Example Example Example ExampleExample Exam- Component name Abbreviation 11 12 13 14 15 16 17 18 19 ple20 Acryl vinyl- VEEA 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.0020.00 20.00 containing monomer Monofunctional LA 10.00 (meth)acrylateMEDOL10 10.00 THFOA 10.00 IBXA 10.00 4HBA 10.00 ACMO 10.0 PEA 30.0030.00 30.00 30.00 30.00 30.00 40.00 30.00 30.00 30.00 PDEGA 10.00 DCPtaA10.00 DCPteA 5.00 5.00 5.00 5.00 10.00 Polyfunctional 2PGA 10.00 10.0010.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 (meth)acrylate DMTCDDA10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 DPHA 5.005.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 Photo- 819 5.00 5.00 5.005.00 5.00 5.00 5.00 5.00 5.00 5.00 polymerization TPO 5.00 5.00 5.005.00 5.00 5.00 5.00 5.00 5.00 5.00 initiator DETX-S 2.00 2.00 2.00 2.002.00 2.00 2.00 2.00 2.00 2.00 Pigment Black 2.00 2.00 2.00 2.00 2.002.00 2.00 2.00 2.00 2.00 Dispersant SOL36000 1.00 1.00 1.00 1.00 1.001.00 1.00 1.00 1.00 1.00 Total 100.00 100.00 100.00 100.00 100.00 100.00100.00 100.00 100.00 100.00

TABLE 7 Example Example Example Example Example Example Example ExampleExample Exam- Component name Abbreviation 21 22 23 24 25 26 27 28 29 ple30 Acryl vinyl- VEEA 20.00 20.00 20.00 20.00 17.00 17.00 30.00 27.0035.00 27.00 containing monomer Monofunctional THFA 20.00 20.00 5.00(meth)acrylate 4HBA 10.00 10.00 15.00 10.00 PEA 30.00 30.00 30.00 30.0020.00 20.00 10.00 30.00 DCPteA 10.00 10.00 5.00 DCPteOEA 10.00 HPPA10.00 10.00 10.00 5.00 5.00 Polyfunctional 2PGA 10.00 10.00 10.00 10.0020.00 20.00 20.00 10.00 (meth)acrylate 3PGA 10.00 10.00 10.00 DMTCDDA10.00 10.00 10.00 10.00 5.00 5.00 5.00 10.00 5.00 DPHA 5.00 5.00 5.005.00 5.00 5.00 UA 5.00 5.00 5.00 5.00 Photo- 819 5.00 5.00 5.00 5.004.00 4.00 5.00 4.00 5.00 4.00 polymerization TPO 5.00 5.00 5.00 5.005.00 5.00 5.00 5.00 5.00 5.00 initiator DETX-S 2.00 2.00 2.00 2.00 1.001.00 2.00 1.00 2.00 1.00 Pigment Black 2.00 2.00 2.00 2.00 2.00 2.002.00 2.00 2.00 2.00 Dispersant SOL36000 1.00 1.00 1.00 1.00 1.00 1.001.00 1.00 1.00 1.00 Total 100.00 100.00 100.00 100.00 100.00 100.00100.00 100.00 100.00 100.00

TABLE 8 Comp. Comp. Comp. Exam- Exam- Exam- Exam- Exam- Exam- Comp.Comp. Comp. Comp. Comp. Component name Abbreviation ple 31 ple 32 ple 33ple 1 ple 2 ple 3 Example 4 Example 5 Example 6 Example 7 Example 8Acryl vinyl- VEEA 27.00 27.00 40.00 5.00 5.00 20.00 80.00 containingmonomer Monofunctional THFA 5.00 5.00 5.00 (meth)acrylate 4HBA 10.005.00 25.00 15.00 PEA 20.00 20.00 22.00 10.00 27.00 30.00 27.00 27.0020.00 DCPteA 5.00 5.00 15.00 15.00 HPPA 5.00 5.00 10.00 10.00Polyfunctional 2PGA 20.00 10.00 30.00 15.00 20.00 10.00 27.00 20.00(meth)acrylate 3PGA 5.00 10.00 5.00 30.00 10.00 20.00 30.00 10.00DMTCDDA 10.00 5.00 5.00 10.00 5.00 10.00 10.00 10.00 DPHA 5.00 5.00 5.005.00 5.00 UA 5.00 5.00 5.00 5.00 5.00 5.00 10.00 Photo- 819 4.00 4.004.00 5.00 4.00 5.00 4.00 4.00 4.00 5.00 5.00 polymerization TPO 5.005.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 initiator DETX-S 1.001.00 1.00 2.00 1.00 2.00 1.00 1.00 1.00 2.00 2.00 Pigment Black 2.002.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 Dispersant SOL360001.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Total 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

TABLE 9 Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp.Comp. Component Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam-Exam- Exam- Reference name Abbreviation ple 9 ple 10 ple 11 ple 12 ple13 ple 14 ple 15 ple 16 ple 17 ple 18 19 Example 1 Acryl vinyl- VEEA45.00 5.00 30.00 17.00 70.00 55.00 20.00 30.00 10.00 20.00 20.00 10.00containing monomer Monofunctional THFA 5.00 5.00 5.00 5.00 5.00(meth)acrylate 4HBA 25.00 5.00 15.00 10.00 15.00 15.00 PEA 20.00 30.0030.00 30.00 15.00 30.00 30.00 15.00 30.00 10.00 10.00 30.00 DCPteA 15.005.00 10.00 10.00 10.00 HPPA 7.00 5.00 10.00 5.00 5.00 Other mono- NVF30.00 functional NVC 30.00 Polyfunctional 2PGA 7.00 20.00 10.00 10.00(meth)acrylate 3PGA 5.00 2.50 2.50 10.00 DMTCDDA 5.00 5.00 10.00 10.0010.00 10.00 DPHA 2.50 2.50 5.00 5.00 5.00 UA 5.00 2.00 5.00 Other poly-TEG-DVE 20.00 functional Photo- 819 4.00 4.00 5.00 4.00 5.00 5.00 5.005.00 4.00 5.00 5.00 4.00 polymerization IPO 5.00 5.00 5.00 5.00 5.005.00 5.00 5.00 5.00 5.00 5.00 5.00 initiator DETX-S 1.00 1.00 2.00 1.002.00 2.00 2.00 2.00 1.00 2.00 2.00 1.00 Pigment Black 2.00 2.00 2.002.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 Dispersant SOL36000 1.00 1.001.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Total 100.00 100.00 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

[Evaluation Item]

The photocurable ink composition for ink jet recording prepared in eachof the examples and the comparative examples was evaluated with respectto curability, extensibility, and curing wrinkles by methods describedbelow.

(1. Curability)

An ink jet printer PX-G5000 (trade name, manufactured by Seiko EpsonCorporation) was used, and a nozzle array was filled with thephotocurable ink composition for ink jet recording of each of theexamples and the comparative examples. A solid pattern image (recordingresolution: 720 dpi×720 dpi) was printed on a PET film (LUMIRROR 125E20(trade name) manufactured by Toray Industries Inc.) at normaltemperature and normal pressure so that ink dots had a medium diameterand the thickness of a coating film on a printed matter was 10 μm. Next,the solid pattern image was cured by irradiating the printed PET film,which was discharged from the printer, with ultraviolet light with anirradiation intensity of 1,500 mW/cm², a wavelength of 395 nm, and anirradiation energy of 200 mJ/cm² using UV-LED of an ultravioletirradiation apparatus. As a result, a recorded material having the solidpattern image printed on the PET film was formed. The “solid patternimage” was an image in which dots were recorded in all pixels in aminimum recording unit region defined by the recording resolution.

The irradiation energy (mJ/cm²) was determined by measuring theirradiation intensity (mW/cm²) on a surface irradiated from the lightsource and multiplying the irradiation intensity by the irradiationduration time (s). The irradiation intensity was measured using anultraviolet ray intensity meter UM-10 and a light receiving unit UM-400(both manufactured by KONICA MINOLTA SENSING, INC.).

The curability of the coating film was evaluated using as an index theirradiation energy when it was tack-free. Whether or not a coating filmbecame tack-free was determined under conditions described below. Thatis, it was determined whether or not an ink adhered to a cotton-tippedswab or whether or not an ink cured product on a recording medium wasscratched. When the ink did not adhere to the cotton-tipped swab and theink cured product on the recording medium was not scratched, the coatingfilm was determined as being “tack-free”. In this case, thecotton-tipped swab used was a Johnson cotton-tipped swab manufactured byJohnson & Johnson Co. Ltd. The number of rubbing cycles was 10, and therubbing strength was a 100-g load.

The evaluation criteria were as follows. The evaluation results areshown in the tables below.

A: Irradiation energy of 200 mJ/cm² or less when the film was tack-free

B: Irradiation energy of over 200 mJ/cm² and 300 mJ/cm² or less when thefilm was tack-free

C: Irradiation energy of over 300 mJ/cm² when the film was tack-free

(2. Extensibility)

The photocurable ink composition for ink jet recording of each of theexamples and the comparative examples was applied over the whole surfaceof a test piece IJ-180-10 of 10 mm×100 mm (trade name, manufactured by3M Corporation, PVC (vinyl chloride) medium) so that the thickness was10 μm. The ink of the coating film was cured by irradiation withultraviolet light with 200 mJ/cm² using UV-LED having an emission peakwavelength of 395 nm, thereby forming a cured film.

The test piece with the cured film formed thereon was stretched fromboth sides thereof in the longitudinal direction using a tensile testerTENSILON (trade name, manufactured by ORIENTEC Co., Ltd.), andelongation percentage (assumed as “100%” when stretched two times) wasmeasured when a crack occurred in the cured film.

The evaluation criteria were as described below. The evaluation resultsare shown in the tables below.

A: Elongation percentage of 100% or more

B: Elongation percentage of over 50% and less than 100%

C: Elongation percentage of 50% or less

(3. Curing Wrinkle)

Evaluation was made using as an index a degree of wrinkling on a surfaceof the solid pattern image formed after the completion of curing forevaluation of curability described above. The degree of wrinkling wasobserved visually and with an optical microscope.

The method for confirming a tack-free state, the solid pattern image,and measurement and calculation of irradiation energy and irradiationintensity were as described above in the evaluation item “Curability”.

The evaluation criteria were as follows. The evaluation results areshown in the tables below.

A: No wrinkle was observed visually and microscopically.

B: No wrinkle was observed visually, but wrinkles were observedmicroscopically.

C: Wrinkles were visually observed.

TABLE 10 Evaluation Example result Example 1 Example 2 Example 3 Example4 Example 5 Example 6 Example 7 Example 8 Example 9 10 Curability B B BA A A A A A A Extensibility A B A A A A A A A A Curing A A B B A A A A AA wrinkle

TABLE 11 Evaluation Example Example Example Example Example ExampleExample Example Example Example result 11 12 13 14 15 16 17 18 19 20Curability A A A A A A A A A A Extensibility A A A A A A A A A A CuringA A A A A A A A A A wrinkle

TABLE 12 Evaluation Example Example Example Example Example ExampleExample Example Example Example result 21 22 23 24 25 26 27 28 29 30Curability A A B B A A A A A A Extensibility A A A A B A B B B B CuringA A A A A B A A B B wrinkle

TABLE 13 Evaluation Exam- Exam- Exam- Comp. Comp. Comp. Comp. Comp.Comp. Comp. Comp. result ple 31 ple 32 ple 33 Example 1 Example 2Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Curability AA B C C C C C C B A Extensibility A B B C B C A A C C C Curing A A B B BB C B A A C wrinkle

TABLE 14 Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp.Comp. Evaluation Exam- Exam- Exam- Example Example Example ExampleExample Example Example Example result ple 9 ple 10 ple 11 12 13 14 1516 17 18 19 Curability B C A A A A C A A A A Extensibility B A A A C C AC A A A Curing C C C C C C C A C C C wrinkle

TABLE 15 Evaluation Reference Reference Reference result Example 1Example 2 Example 3 Curability A A A Extensibility B A A Curing A A Awrinkle

The above results indicate that the ink composition containing thepolymerizable compounds and the photopolymerization initiator, thepolymerizable compounds including 10 to 40% by mass of the vinyl ethergroup-containing (meth)acrylate represented by the general formula (I),20 to 60% by mass of the monofunctional (meth)acrylate, and 10 to 40% bymass of the polyfunctional (meth)acrylate is, as compared with the inkcomposition for which this is not true, excellent in curability andextensibility of a cured film and capable of preventing the occurrenceof curing wrinkles.

In detailed consideration, it was found that the ink compositioncontaining the vinyl ether group-containing (meth)acrylate representedby the general formula (I) is, as compared with the ink composition notcontaining this, excellent in curability (each of the examples andComparative Examples 1 and 3 to 5). Also, it was found that the inkcomposition containing 10% by mass or more (40% by mass or less) of thevinyl ether group-containing (meth)acrylate is, as compared with the inkcomposition for which this is not true, excellent in curability (referto each example and Comparative Examples 2, 6, and 10). Further, it wasfound that the ink composition containing 40% by mass or less (10% bymass or more) of the vinyl ether group-containing (meth)acrylate is, ascompared with the ink composition for which this is not true, excellentin the prevention of occurrence of curing wrinkles and also satisfactoryin curability and extensibility of the cured film (refer to each exampleand Comparative Examples 9, 8, 13, and 14).

In addition, it was found that the ink composition containing themonofunctional (meth)acrylate is, as compared with the ink compositionnot containing this, excellent at least in extensibility of the curedfilm and is more excellent in curability and capable of preventing theoccurrence of curing wrinkles when a thick film is cured (refer to eachexample and Comparative Examples 6 and 8). Further, it was found thatthe ink composition containing 20% by mass or more (60% by mass or less)of the monofunctional (meth)acrylate is, as compared with the inkcomposition for which this is not true, excellent in extensibility ofthe cured film (refer to each example and Comparative Examples 16, 1,and 13).

Further, it was found that the ink composition containing 20% by mass ormore (60% by mass or less) of the monofunctional (meth)acrylate iscapable of preventing the occurrence of curing wrinkles as compared withthe ink composition containing 20% by mass or more (60% by mass or less)of the monofunctional polymerizable monomers but containing less than20% by mass of the monofunctional (meth)acrylate (refer to each exampleand Comparative Examples 18 and 19). This reveals that ComparativeExamples 18 and 19 have good results of extensibility but poor resultsof curing wrinkles. This result is estimated to be due to NVF and NVC.Specifically, NVF and NVC have vinyl groups as polymerizable reactivegroups and are thus very excellent in reactivity as compared with acrylgroup-containing monomers (assuming that they are used in combinationwith acrylate). Therefore, it is supposed that curing unevenness easilyoccurs due to a difference in reaction rate between vinyl groups andacryl groups, thereby easily causing wrinkles. Similarly, VEEA containsa vinyl ether group and thus may cause curing wrinkles due to adifference in reaction rate from an acryl group when added excessively(Comparative Example 13).

Further, it was found that the ink composition containing 60% by mass orless (20% by mass or more) of the monofunctional (meth)acrylate is, ascompared with the ink composition for which this is not true, capable ofpreventing the occurrence of curing wrinkles (refer to each example andComparative Examples 17, 4, 5, 10, and 12).

In addition, it was found that the ink composition containing thepolyfunctional (meth)acrylate is, as compared with the ink compositionnot containing this, excellent in at least the prevention of theoccurrence of curing wrinkles and good in curability and extensibilityof the cured film (refer to each example and Comparative Examples 10 and12 to 14). Further, it was found that the ink composition containing 10%by mass or more (40% by mass or less) of the polyfunctional(meth)acrylate is, as compared with the ink compositions for which thisis not true, capable of preventing the occurrence of curing wrinkles(refer to each example and Comparative Examples 11, 4, and 8). Further,it was found that the ink composition containing 10% by mass or more(40% by mass or less) of the polyfunctional (meth)acrylate is capable ofpreventing the occurrence of curing wrinkles and is excellent incurability as compared with the ink composition containing 10% by massor more (40% by mass or less) of the polyfunctional polymerizablecompounds but containing less than 10% by mass of the polyfunctional(meth)acrylate (refer to each example and Comparative Example 15).Further, it was found that the ink composition containing 40% by mass orless (10% by mass or more) of the polyfunctional (meth)acrylate is, ascompared with the ink composition for which this is not true, excellentin extensibility of the cured film and curability (refer to each exampleand Comparative Examples 7, 1, 3, and 6).

Further, although Comparative Example 17 is not excellent in theprevention of the occurrence of curing wrinkles, Reference Example 1 notcontaining the pigment and the dispersant of Comparative Example 17 isexcellent in the prevention of the occurrence of curing wrinkles butcannot be used for recording color images because of the absence of thecolorant. This reveals that the ink composition of each of the examplesis excellent in curability, extensibility, and the prevention of theoccurrence of curing wrinkles and can be used for recording colorimages.

Reference Examples 2 and 3 using the ink compositions of ComparativeExamples 11 and 17, respectively, were evaluated by the same method asin Comparative Examples 11 and 17 except that each of the evaluationsamples was formed by irradiation using a metal halide lamp (irradiationintensity: 1,000 mW/m²) in place of UV-LED. Although ComparativeExamples 11 and 17 were not excellent in the prevention of occurrence ofcuring wrinkles, Reference Examples 2 and 3 were excellent in theprevention of occurrence of curing wrinkles. However, the PET film wasdeformed due to the heat generated from the metal halide. This revealsthat the ink composition of each of the examples is excellent incurability, extensibility, and the prevention of the occurrence ofcuring wrinkles and can be used for forming an excellent recordedmaterial without thermal deformation of a film by using LED forirradiation.

The entire disclosure of Japanese Patent Application No.: 2012-008704,filed Jan. 19, 2012 and 2011-151770, filed Jul. 8, 2011 and 2011-200809,filed Sep. 14, 2011 are expressly incorporated by reference herein.

What is claimed is:
 1. A photocurable ink composition for ink jetrecording, comprising: polymerizable compounds; a photopolymerizationinitiator; and a colorant, wherein the polymerizable compounds include avinyl ether group-containing (meth)acrylate represented by generalformula (I):CH₂═CR¹—COOR²—O—CH═CH—R²  (I) (wherein R¹ is a hydrogen atom or a methylgroup, R² is a divalent organic residue having 2 to 20 carbon atoms, andR³ is a hydrogen atom or a monovalent organic residue having 1 to 11carbon atoms) and phenoxyethyl (meth)acrylate.
 2. The photocurable inkcomposition for ink jet recording according to claim 1, wherein thecontent of the phenoxyethyl (meth)acrylate is 9 to 60% by mass relativeto the total mass of the ink composition.
 3. The photocurable inkcomposition for ink jet recording according to claim 1, wherein thephotopolymerization initiator contains 7% by mass or more of anacylphosphine oxide compound relative to the total mass of the inkcomposition.
 4. The photocurable ink composition for ink jet recordingaccording to claim 1, wherein the photopolymerization initiator contains7 to 15% by mass of an acylphosphine oxide compound relative to thetotal mass of the ink composition.
 5. The photocurable ink compositionfor ink jet recording according to claim 1, wherein thephotopolymerization initiator contains 10 to 15% by mass of anacylphosphine oxide compound relative to the total mass of the inkcomposition.
 6. The photocurable ink composition for ink jet recordingaccording to claim 1, wherein the vinyl ether group-containing(meth)acrylate is 2-(vinyloxyethoxy)ethyl (meth)acrylate.
 7. Thephotocurable ink composition for ink jet recording according to claim 1,wherein the content of the vinyl ether group-containing (meth)acrylateis 10 to 60% by mass relative to the total mass of the ink composition.8. The photocurable ink composition for ink jet recording according toclaim 1, wherein the ink composition is cured by irradiation withultraviolet light with an emission peak wavelength in a range of 350 to420 nm and an irradiation energy of 300 mJ/cm² or less.
 9. An ink jetrecording method comprising: ejecting the photocurable ink compositionfor ink jet recording according to claim 1 onto a recording medium; andcuring the ejected photocurable ink composition for ink jet recording byultraviolet irradiation.
 10. A photocurable ink composition for ink jetrecording, comprising: polymerizable compounds; a photopolymerizationinitiator; and a colorant, wherein the polymerizable compounds include,relative to the total mass of the ink composition, 10 to 40% by mass ofa vinyl ether group-containing (meth)acrylate represented by generalformula (I):CH₂═CR¹—COOR²—O—CH═CH—R³  (I) (wherein R¹ is a hydrogen atom or a methylgroup, R² is a divalent organic residue having 2 to 20 carbon atoms, andR³ is a hydrogen atom or a monovalent organic residue having 1 to 11carbon atoms), 20 to 60% by mass of a monofunctional (meth)acrylate(excluding the vinyl ether group-containing (meth)acrylate), and 10 to40% by mass of a polyfunctional (meth)acrylate.
 11. The photocurable inkcomposition for ink jet recording according to claim 10, wherein themonofunctional (meth)acrylate contains 10 to 60% by mass of phenoxyethyl(meth)acrylate relative to the total mass of the ink composition. 12.The photocurable ink composition for ink jet recording according toclaim 10, wherein the photopolymerization initiator contains 6 to 13% bymass of an acylphosphine oxide compound relative to the total mass ofthe ink composition.
 13. The photocurable ink composition for ink jetrecording according to claim 10, wherein the content of themonofunctional (meth)acrylate is 20 to 40% by mass relative to the totalmass of the ink composition.
 14. The photocurable ink composition forink jet recording according to claim 10, wherein the content of thepolyfunctional (meth)acrylate is 20 to 30% by mass relative to the totalmass of the ink composition.
 15. The photocurable ink composition forink jet recording according to claim 10, wherein the ink composition iscured by irradiation with ultraviolet light with an emission peakwavelength in a range of 350 to 420 nm and an irradiation energy of 300mJ/cm² or less.
 16. The photocurable ink composition for ink jetrecording according to claim 10, wherein the vinyl ethergroup-containing (meth)acrylate is 2-(vinyloxyethoxy)ethyl(meth)acrylate.
 17. The photocurable ink composition for ink jetrecording according to claim 10, wherein the primary skin irritationindex of the monofunctional (meth)acrylate is 0 to
 4. 18. An ink jetrecording method using the photocurable ink composition for ink jetrecording according to claim 10, the method comprising: causing thephotocurable ink composition for ink jet recording to adhere to arecording medium; and irradiating, using a light-emitting diode, theadhering photocurable ink composition for ink jet recording withultraviolet light with an emission peak wavelength in a range of 350 to420 nm.
 19. The ink jet recording method according to claim 18, whereinthe irradiation energy of the ultraviolet light is 300 mJ/cm² or less.